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¹ Physiological Laboratory, Department of Physiology, Development & Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK

	Abstract

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During the response of vertebrate olfactory receptor cells to stimulation, Ca²⁺ enters the cilia via cyclic nucleotide-gated channels and is extruded by Na⁺–Ca²⁺ exchange. The rise in Ca²⁺ concentration opens a Ca²⁺-activated Cl^– conductance which carries most of the inward receptor current. The dependence of Ca²⁺ extrusion upon external Na⁺ concentration was studied by using the falling phase of the Ca²⁺-activated Cl^– current following a brief exposure to the phosphodiesterase inhibitor IBMX to monitor indirectly the decay in intraciliary Ca²⁺ concentration. External Na⁺ concentration was reduced by partial substitution with guanidinium, an ion which permeates the cyclic nucleotide-gated channel but does not support Na⁺–Ca²⁺ exchange. The time constant describing the decay in current following IBMX stimulation was surprisingly little affected by substitution of external Na⁺, being substantially retarded only when its concentration was reduced to a third or less of its normal value in Ringer solution. When the cilia were returned to Ringer solution after a period in reduced-Na⁺ solution, the time constant for the final decay of current was similar to that seen when returning immediately to IBMX-free Ringer solution. This observation suggests that Ca²⁺ extrusion via Na⁺–Ca²⁺ exchange dominates the falling phase of the response to IBMX, which can therefore be used to assess exchanger activity. Rate constants derived from the time constants for current decay at different external Na⁺ concentrations could be fitted by the Hill equation with a K_d of 54 ± 4 mM and Hill coefficient of 3.7 ± 0.4. The cooperativity of the dependence upon external Na⁺ concentration indicates that at least three Na⁺ ions enter for each exchanger cycle, while the high affinity for external Na⁺ contrasts with the photoreceptor and cardiac exchangers. The functional importance of this observation is that the relative insensitivity of the Na⁺–Ca²⁺ exchanger to external Na⁺ concentration allows normal response termination even following partial dilution or concentration of the olfactory mucus.

(Received 27 February 2007; accepted after revision 19 March 2007; first published online 22 March 2007)
Corresponding author H. R. Matthews: Physiological Laboratory, Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK. Email: hrm1{at}cam.ac.uk

	Introduction

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When a vertebrate olfactory receptor cell is exposed to odour, the G protein-coupled transduction cascade stimulates production of cAMP by adenylyl cyclase (reviewed by Schild & Restrepo, 1998; Firestein, 2001; Zufall & Munger, 2001), opening cyclic nucleotide-gated channels and allowing an influx of Ca²⁺ (Frings & Lindemann, 1991; Leinders-Zufall et al. 1997). The rise in Ca²⁺ concentration within the cilia opens a Ca²⁺-activated Cl^– conductance which greatly augments the inward receptor current (Kleene & Gesteland, 1991; Kurahashi & Yau, 1993; Kleene, 1997). The Ca²⁺ which enters during stimulation is principally extruded by Na⁺–Ca²⁺ exchange, which lowers the Ca²⁺ concentration allowing closure of Ca²⁺-activated Cl^– channels and termination of the response (Reisert & Matthews, 1998).

While the importance of Na⁺–Ca²⁺ exchange for the control of response dynamics and sensitivity has been clearly demonstrated in the olfactory receptors of both amphibia (Reisert & Matthews, 1999, 2001b,c) and mammals (Reisert & Matthews, 2001a), little is known about the detailed properties of the olfactory exchanger itself. The driving gradient for Ca²⁺ extrusion depends crucially on the Na⁺ concentration in the mucus surrounding the olfactory cilia. However, especially in an amphibious species the mucus composition is potentially under threat from dilution by water thereby decreasing ionic concentrations, while mucus desiccation and an increase in ionic strength are possible in terrestrial species. Cholinergic stimulation has been shown to decrease the concentration of Na⁺ in mouse tracheal surface fluid and increase its concentration in nasal fluid (Kozlova et al. 2005). In contrast, tracheal fluid Na⁺ concentration is increased in cystic fibrosis (Kozlova et al. 2005). If the resulting changes in Na⁺ gradient were to affect substantially the rate of exchange, changes in response kinetics might ensue. We have therefore investigated the effect of extracellular Na⁺ concentration on the extrusion of Ca²⁺ in frog olfactory receptors using the suction pipette technique. Our results demonstrate that the olfactory Na⁺–Ca²⁺ exchanger is only modestly affected until external Na⁺ concentration is reduced substantially below the normal value in Ringer solution, in contrast to the photoreceptor and cardiac exchangers. This high affinity for external Na⁺ defends the kinetics of olfactory response recovery against changes in Na⁺ concentration in the olfactory mucus. Preliminary results from this study have been reported to the Association for Chemoreception Sciences (Antolin & Matthews, 2006).

	Methods

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Preparation

Isolated olfactory receptor cells were obtained as previously described (Reisert & Matthews, 1998, 1999). Frogs (Rana temporaria) were killed according to Schedule 1 of the Animals (Scientific Procedures) Act 1986 by stunning by cranial concussion followed by rostral and caudal pithing. The olfactory epithelia were dissected and placed receptor side up on a layer of cured silicone rubber (Sylgard 184, Dow Corning, Wiesbaden, Germany) in a Petri dish filled with Ringer solution. Olfactory receptor cells were isolated mechanically by lightly cutting the olfactory epithelium with a piece of razor blade. The resulting cell suspension was collected with a 200 µl pipette, triturated several times in a microcentrifuge tube, and transferred to the recording chamber on the stage of an inverted microscope with phase contrast optics (Nikon TMS; Nikon Ltd, Kingston, UK). Cells were allowed to settle on the floor of the recording chamber for 30 min before bath perfusion commenced.

Suction pipette recording

Receptor current responses to stimulation were recorded using the suction pipette technique as previously described (Reisert & Matthews, 1998, 1999). Typical suction pipette diameter ranged from 5 to 7 µm, corresponding to an open pipette resistance of 1–2 M. The cell body of an isolated olfactory receptor cell was drawn into the suction pipette leaving the cilia exposed to the superfusing solution, elevating the seal resistance at the pipette tip (2–7 M Reisert & Matthews, 1999) by at least 2–3-fold (Reisert & Matthews, 2001c), and allowing the receptor current to be recorded. The suction pipette current was recorded with a patch clamp amplifier (Warner PC-501A, Warner Instruments, Hamden, CT, USA) and digitized over a relatively low bandwidth (filtered DC–50 Hz, sampled at 200 Hz) by a PC equipped with an intelligent interface card (Cambridge Research Systems, Rochester, UK) in order to analyse the receptor current. Traces are plotted according to the convention that current flowing into the suction pipette is of negative sign, representing the inward receptor current flowing across the ciliary membrane.

Solutions and solution changes

Amphibian Ringer solution contained 111 mM NaCl, 2.5 mM KCl, 1.6 mM MgCl₂, 1 mM CaCl₂, 3 mM Hepes, 10 mM glucose, and its pH was adjusted to 7.7 with NaOH. The solution also included 0.01 mM EDTA to chelate impurity heavy metal ions (Lamb et al. 1986). Reduced Na⁺ solutions were prepared by partial substitution of guanidinium chloride for NaCl; the pH was adjusted to 7.7 with approximately 1.7 mM TMAOH. The phosphodiesterase inhibitor 3-isobutyl-1 methylxanthine (IBMX; Sigma, Gillingham, UK) was dissolved in Ringer solution when required at the concentrations indicated in the text. Solutions with elevated Na⁺ concentration were prepared by addition of Na-gluconate (see Fig. 6).

View larger version (8K): [in this window] [in a new window]   Figure 6.  Dependence of time constant for receptor current recovery on external [Na+] A, mean time constants for single exponential curves fitted to receptor current recovery in solutions with modified Na+ concentration following IBMX exposures of 1 s (, as in Fig. 4) or 2 s () duration. Data have been normalized for each cell to the time constant measured in normal Ringer (111 mM [Na+]). Data points represent the means of 3–18 cells; error bars denote standard errors of the mean. B, rate constants, calculated as the reciprocal of the mean time constants for the 1 s IBMX exposures in A, normalized to the rate constant in normal Ringer solution, which was measured in each cell. Fitted curve represents the Hill equation with Kd = 62.3 mM and n = 3.24, with minimum rate constrained to zero and a maximum normalized rate of 1.15, fitted by a weighted Marquardt–Levenberg least squares algorithm.

View larger version (10K): [in this window] [in a new window]   Figure 1.  Procedure for junction current subtraction Suction pipette recordings from an isolated olfactory receptor cell in response to 1 s stimulation with Ringer solution containing 500 µM IBMX. Following IBMX stimulation the cilia were returned to Ringer solution either immediately (A) or after 1 s exposure to a solution in which the Na+ concentration had been reduced to 33 mM (low Na+) by equimolar substitution with guanidinium (B). Each trace is the average of 2 or 3 trials.

	Results

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View larger version (9K): [in this window] [in a new window]   Figure 2.  The time constant for receptor current recovery reflects Ca2+ extrusion by Na+–Ca2+ exchange Suction pipette recordings from an isolated olfactory receptor cell in response to 1 s stimulation with Ringer solution containing 500 µM IBMX. Same cell as Figure 1. Following IBMX stimulation the cilia were returned to Ringer solution either immediately (A) or following exposure for 1 s (B), 2 s (C), or 3 s (D) to a solution in which the Na+ concentration had been reduced to 33 mM (low Na+) by equimolar replacement with guanidinium. In each case the rapid decay of receptor current upon the return to Ringer solution has been fitted with a single exponential of time constant A: 0.521 s; B: 0.692 s; C: 0.561 s; D: 0.498 s. Interrupted curves in B–D reproduce the exponential fit to A for comparison. Each trace is the average of 2 or 3 trials and has been junction corrected.

Figure 3 shows results from such an experiment, in which the effect of 5 mM Ni²⁺ on receptor current decay was examined following IBMX stimulation. As with reduced external Na⁺ concentration, exposure of the cilia to Ni²⁺ retarded response recovery until the cilia were returned to normal Ringer solution, without any substantial effect on the time constant of the subsequent current decay.

View larger version (9K): [in this window] [in a new window]   Figure 3.  Receptor current recovery is retarded when Na+–Ca2+ exchange is inhibited by Nio2+ Suction pipette recordings from an isolated olfactory receptor cell in response to 1 s stimulation with Ringer solution containing 500 µM IBMX. Following IBMX stimulation the cilia were returned to Ringer either immediately (A) or following exposure for 2 s (B) or 3 s (C) to a solution which included 5 mM Nio2+. In each case the rapid decay of receptor current upon the return to Ringer solution has been fitted with a single exponential of time constant A: 0.434 s; B: 0.335 s; C: 0.454 s. Interrupted curves in B and C reproduce the exponential fit to A for comparison. Each trace is the average of 2–3 trials and has been junction corrected.

View larger version (22K): [in this window] [in a new window]   Figure 4.  The time constant for receptor current recovery upon the return to Ringer solution is little affected by the duration of prior inhibition of Na+–Ca2+ exchange Collected data from experiments in which the cilia of an isolated olfactory receptor were exposed, following IBMX stimulation, to reduced Na+ concentration (as in Fig. 2; mean of 19–20 cells) or Ni2+ (as in Figure 3; mean of 10–11 cells) for the durations indicated before the return to Ringer solution. In each case time constants have been normalized for each cell to the value obtained upon the immediate return to Ringer solution. Error bars represent standard errors of the mean.

The dependence of Ca²⁺ extrusion upon external Na⁺ concentration was studied by using the decay of the receptor current to monitor indirectly the decay in intraciliary Ca²⁺ concentration following a brief exposure to IBMX. Figure 5A shows results from such an experiment in which the cilia were first exposed for 1 s to 100 µM IBMX, and then returned to an IBMX-free solution of reduced Na⁺ concentration. The final decay of current proved to be surprisingly little affected by partial replacement of external Na⁺, being substantially retarded only when its concentration was reduced to a third or less of its normal value in Ringer solution. These data have been normalized and replotted on an expanded time base in Fig. 5B. The decline in current following the reduction in Na⁺ concentration has been fitted by a single decaying exponential function. The time constant for the fitted exponential decay increased monotonically in a graded manner as Na⁺ was progressively replaced with guanidinium, being retarded for this cell by a factor of 17.4 for a 10-fold fall in [Na⁺].

View larger version (16K): [in this window] [in a new window]   Figure 5.  Effect of external Na+ concentration on receptor current recovery A, suction pipette recordings from an isolated olfactory receptor cell in response to 1 s stimulation with Ringer solution containing 100 µM IBMX. Following IBMX stimulation the cilia were returned either to Ringer solution, or to partially guanidinium-substituted solutions of reduced Na+ concentration as indicated beside each trace. B, final decay of receptor currents in low-Na+ solution from A, normalized to the value just following the solution change. Individual traces have been zeroed as in Fig. 5A to the initial baseline before the IBMX stimulus; note slight baseline drift. In each case the decay of receptor current has been fitted with a single exponential of time constant 99 mM: 0.067 s; 66 mM: 0.125 s; 33 mM: 0.285 s; 11 mM: 1.46 s. Time constant in normal Ringer solution 0.084 s. Each trace is the average of 2–3 trials and has been junction corrected.

The filled symbols for 1 s IBMX stimulation have been transformed to rate constants in Fig. 6B, calculated as the reciprocal of the time constants, and normalized to the rate constant in normal Ringer solution. It can be seen that increasing the sodium concentration above that in normal Ringer solution by addition of sodium gluconate did not further elevate the rate constant for current decay. The data have been fitted with the Hill equation with a K_d of 54 ± 4 mM and Hill coefficient of 3.7 ± 0.4, yielding a characteristic sigmoidal variation with Na⁺ concentration when plotted in semilogarithmic coordinates. These results indicate that the olfactory exchanger possesses a relatively high affinity for Na⁺ at its external face.

	Discussion

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Calcium ions are known to play a crucial role in olfactory transduction, not only as an excitatory messenger by opening Ca²⁺-activated Cl^– channels, but also through feedback actions on cyclic nucleotide-gated channels and other components of the transduction cascade (reviewed by Matthews & Reisert, 2003). Ca²⁺ enters the cilia during stimulation as the main component of the current through cyclic nucleotide-gated channels, and is believed to be extruded principally by Na⁺–Ca²⁺ exchange (Jung et al. 1994; Reisert & Matthews, 1998), which lowers the Ca²⁺ concentration during recovery (Reisert & Matthews, 1998). While complementary mechanisms may contribute to Ca²⁺ extrusion from dendrite (Jung et al. 1994) and soma (Leinders-Zufall et al. 1997), it seems unlikely that these contribute to ciliary Ca²⁺ homeostasis in the short term (Leinders-Zufall et al. 1997; Leinders-Zufall et al. 1998), since the cilia are diffusionally remote from these more proximal structures (Lindemann, 2001). While it might appear superficially attractive to study the kinetics of Ca²⁺ extrusion by recording the electrogenic currents carried by the exchanger itself, our previous work has demonstrated that these are of very small amplitude (< 2 pA, Antolin & Matthews, 2004), making such measurements unreliable. Direct measurement of calcium concentration is impractical in frog olfactory receptors, since their olfactory cilia fail to load with tetracarboxylate calcium indicators (S. Antolin, J. Reisert & H. R. Matthews, unpublished observations), most probably due to their extrusion by multidrug resistance anion transporters which have been shown to be present in the olfactory cilia of Xenopus (Manzini & Schild, 2003). We have therefore adopted instead an indirect approach.

We used the phosphodiesterase inhibitor IBMX to elevate the cAMP concentration within the olfactory cilia, thereby enabling Ca²⁺ entry through cyclic nucleotide-gated channels, and examined the subsequent decay of current upon its withdrawal. At the peak of the response to IBMX, nearly 80% of the receptor current can be inhibited by the Ca²⁺-activated Cl^– channel blocker niflumic acid (Antolin, 2006), indicating that at the time of response recovery the vast majority of the current is likely to flow through this conductance. The final decline in receptor current could be delayed by either substantial reduction of the external Na⁺ concentration (Fig. 2) or by external application of Ni²⁺ (Fig. 3) without change in the final decay kinetics upon the return to normal Ringer solution (Fig. 4). Since either of these manipulations would be expected to inhibit Na⁺–Ca²⁺ exchange, these results imply that the recovery of the response to IBMX is dominated by the kinetics of Ca²⁺ extrusion, governing the decline in [Ca²⁺]_i which leads to the progressive closure of Ca²⁺-activated Cl^– channels. Since the magnitude of this conductance depends approximately on the square of the Ca²⁺ concentration (Kleene, 1997), the time constant for current decay is likely to reflect about half the time constant for the extrusion of Ca²⁺ by Na⁺–Ca²⁺ exchange. The kinetics of Ca²⁺ extrusion will depend not only upon the sodium gradient, but also on the number of exchanger molecules and the native calcium buffering properties of the cytoplasm (see e.g. Lagnado et al. 1992); however, these factors will normally remain constant for any given cell.

We found that the kinetics of current decay following IBMX stimulation depended only rather weakly on external Na⁺ concentration (Fig. 5). In order to prolong substantially the time constant for recovery, it was necessary to reduce the external Na⁺ concentration to a third or less of its value in normal Ringer. We infer that the rate constant for Na⁺–Ca²⁺ exchange must exhibit a similarly shallow dependence upon Na⁺ concentration, implying a high affinity for Na⁺ at its external site. Since our experiments were not carried out under clamped conditions, the voltage experienced by the exchanger will have varied continuously during response recovery. This might be expected to affect the electrogenic exchanger, not only through a change in the driving electrochemical gradient, but also perhaps through voltage dependence of external Na⁺ binding (Lagnado et al. 1988). However, in our experiments the external Na⁺ concentration would not be expected to affect the intraciliary voltage directly, since only the cilia were exposed to reduced Na⁺ concentration and their conductance is dominated by the opening of Ca²⁺-actived Cl^– channels during response recovery (Fig. 2 and Antolin, 2006). In contrast, the cell body was in contact throughout the experiment with the normal Ringer solution within the pipette. Since the receptor current decayed exponentially back towards zero, the voltage would be expected to have followed a common trajectory during extrusion of the Ca²⁺ load at each Na⁺ concentration, with only a corresponding variation in time scale. Therefore, the perturbing effect of voltage changes would be expected to be equivalent in each case, allowing direct comparison between the time constants for current decay.

Consequently, comparison of the time constants for current recovery allows the dependence of exchanger rate upon external Na⁺ concentration to be inferred. The power-law dependence of Ca²⁺-activated Cl^– channel opening upon Ca²⁺ concentration implies a fixed scaling relationship between the time constants for current decay and exchange extrusion. The Hill analysis of the normalized reciprocal time constant as a function of Na⁺ concentration (Fig. 6) therefore represents the effect of Na⁺ on the rate constant of Ca²⁺ extrusion by olfactory Na⁺–Ca²⁺ exchange.

Although the photoreceptor exchanger (NCKX1) and the cardiac exchanger (NCX) appear to have evolved independently (Nicoll et al. 1990; Reilander et al. 1992), both of these two Ca²⁺ extrusion mechanisms are more strongly affected by variations of Na⁺ concentration in the external medium than is the olfactory exchanger. Our results show that for the frog olfactory exchanger, a reduction in external Na⁺ concentration to 66 mM increased the time constant by only 1.5-fold, while a reduction to 33 mM increased it by approximately 6-fold. In contrast, in salamander photoreceptors, reduction of external Na⁺ to 55 mM by substitution with Li⁺ slows Na⁺–Ca²⁺,K⁺ exchange approximately 5-fold, while at an external Na⁺ concentration of 35 mM a 16-fold slowing ensues (Hodgkin & Nunn, 1987). This greater sensitivity to reduction in external Na⁺ concentration corresponds to a dissociation constant for the photoreceptor exchanger of 139 mM at depolarized potentials, decreasing to 109 mM at potentials closer to the neuronal resting potential (Lagnado et al. 1988). This is approximately twice the Na⁺ dissociation constant of 54 ± 4 mM which we obtain for the olfactory exchanger. Since the voltage was free to vary in our experiments, we cannot assess whether the external Na⁺ binding site experiences a fraction of the membrane field, as is the case for the photoreceptor exchanger (Lagnado et al. 1988). If this were the case, our value would represent the weighted mean for the voltage range over which response recovery takes place. In cardiac myocytes, the cardiac exchanger is believed to operate near thermodynamic equilibrium, to establish a cytoplasmic Ca²⁺ concentration which depends upon the membrane potential and the Na⁺ gradient (reviewed by Hilgemann, 2004). In consequence a striking effect on the excitation–contraction cycle in the heart occurs with only small changes in Na⁺ concentration. Measurement of the Na⁺ affinity at the cardiac Na⁺–Ca²⁺ exchanger's external site reveals a dissociation constant of 87.5 mM (Kimura et al. 1987), a value rather higher than we observe for the olfactory exchanger. In contrast to the photoreceptor and cardiac exchangers, neuronal Na⁺–Ca²⁺ exchangers of both the NCX (Sanchez-Armass & Blaustein, 1987) and NCKX2 (Dong et al. 2001) families exhibit considerably lower dissociation constants and hence higher affinities for external Na⁺ (reviewed by Blaustein & Lederer, 1999; Schnetkamp, 2004). Consequently, the comparatively high affinity of the olfactory exchanger for external Na⁺ does not place it unequivocally in one or the other family.

The Hill coefficient of 3.7 ± 0.4 which we obtained from the olfactory exchanger for the binding of Na⁺ at its external site suggests that at least three Na⁺ ions are likely to enter the cilia for each exchanger cycle. However, this value does not allow the olfactory exchanger to be assigned unequivocally to the NCX rather than the NCKX family of Na⁺–Ca²⁺ exchangers, since the photoreceptor NCKX1 exchanger also exhibits a similar Hill coefficient of around three for external Na⁺, suggesting that the fourth Na⁺ binding site is not equivalent to the other three (Lagnado et al. 1988). Earlier studies unfortunately do not help to resolve this issue. Olfactory cilia are labelled by an antibody raised against the bovine rod Na⁺–Ca²⁺,K⁺ exchanger, suggesting that the olfactory exchanger might be a member of the NCKX family also (Noe et al. 1997). However, the olfactory exchanger can be reversed without a requirement for external K⁺ (Reisert et al. 2003), in contrast to the photoreceptor exchanger (Cervetto et al. 1989), a result more consistent with membership of the NCX family. But even this cannot be regarded as conclusive, since the requirement for external K⁺ can be removed by a single point mutation in the NCKX2 exchanger (Kang et al. 2005). Consequently, conclusive identification of the identity of the olfactory exchanger is likely to require a more molecular approach. However, a recent in situ hybridization study has suggested that multiple isoforms of both NCX and NCKX may be present in multiple splice variants within mammalian olfactory receptor cells (Pyrski et al. 2007), further complicating the understanding of the functional role of these exchangers in olfactory transduction.

Our finding that the rate of Ca²⁺ extrusion by Na⁺–Ca²⁺ exchange was only modestly affected by extracellular Na⁺ until its concentration fell to 30% of its value in Ringer solution has important functional implications for the recovery of the olfactory response. This range of relative Na⁺ insensitivity included the value of 55 mM, the Na⁺ concentration reported to be present in both frog and rat olfactory mucus (Joshi et al. 1987; Reuter et al. 1998). Consequently, although the recovery phase of the olfactory receptor cell response appears to be dominated by the rate of Ca²⁺ extrusion from the cilia, response kinetics would be expected to be only marginally affected by modest increases or decreases in mucus Na⁺ concentration from this value, as might arise through desiccation or dilution.

	References

Top Abstract Introduction Methods Results Discussion References

 
Antolin S (2006). Sodium-calcium exchange in amphibian olfactory receptor cells. PhD Thesis, University of Cambridge.

Antolin S & Matthews HR (2004). Characterisation of the electrogenic Na⁺-Ca²⁺ exchange current in frog olfactory receptor cells. J Physiol 555.P, C160.

Antolin S & Matthews HR (2006). Effect of external Na⁺ on Na-Ca exchange-mediated current recovery in frog ORNs. Association for Chemoreception Sciences meeting abstract, A37.

Blaustein MP & Lederer WJ (1999). Sodium/calcium exchange: its physiological implications. Physiol Rev 79, 763–854.[Abstract/Free Full Text]

Borisy FF, Ronnett GV, Cunningham AM, Juilfs D, Beavo J & Snyder SH (1992). Calcium/calmodulin-activated phosphodiesterase expressed in olfactory receptor neurons. J Neurosci 12, 915–923.[Abstract]

Brommundt G & Kavaler F (1987). La³⁺, Mn²⁺, and Ni²⁺ effects on Ca²⁺ pump and on Na⁺-Ca²⁺ exchange in bullfrog ventricle. Am J Physiol Cell Physiol 253, C45–C51.[Abstract/Free Full Text]

Cervetto L, Lagnado L, Perry RJ, Robinson DW & McNaughton PA (1989). Extrusion of calcium from rod outer segments is driven by both sodium and potassium gradients. Nature 337, 740–743.[CrossRef][Medline]

Cervetto L & McNaughton PA (1986). The effects of phosphodiesterase inhibitors and lanthanum ions on the light-sensitive current of toad retinal rods. J Physiol 370, 91–109.[Abstract/Free Full Text]

Dong H, Light PE, French RJ & Lytton J (2001). Electrophysiological characterization and ionic stoichiometry of the rat brain K⁺-dependent Na⁺/Ca²⁺ exchanger, NCKX2. J Biol Chem 276, 25919–25928.[Abstract/Free Full Text]

Fain GL, Lamb TD, Matthews HR & Murphy RLW (1989). Cytoplasmic calcium concentration as the messenger for light adaptation in salamader rods. J Physiol 416, 215–243.[Abstract/Free Full Text]

Firestein S (2001). How the olfactory system makes sense of scents. Nature 413, 211–218.[CrossRef][Medline]

Frings S & Lindemann B (1991). Current recording from sensory cilia of olfactory receptor cells in situ. I. The neuronal response to cyclic nucleotides. J Gen Physiol 97, 1–16.[Abstract/Free Full Text]

Hilgemann DW (2004). New insights into the molecular and cellular workings of the cardiac Na⁺/Ca²⁺ exchanger. Am J Physiol Cell Physiol 287, C1167–C1172.[Abstract/Free Full Text]

Hodgkin AL & Nunn BJ (1987). The effect of ions on sodium-calcium exchange in salamander rods. J Physiol 391, 371–398.[Abstract/Free Full Text]

Iwamoto T & Shigekawa M (1998). Differential inhibition of Na⁺/Ca²⁺ exchanger isoforms by divalent cations and isothiourea derivative. Am J Physiol Cell Physiol 275, C423–C430.[Abstract/Free Full Text]

Joshi H, Getchell ML, Zielinski B & Getchell TV (1987). Spectrophotometric determination of cation concentrations in olfactory mucus. Neurosci Lett 82, 321–326.[CrossRef][Medline]

Jung A, Lischka FW, Engel J & Schild D (1994). Sodium/calcium exchanger in olfactory receptor neurons of Xenopus laevis. Neuroreport 5, 1741–1744.[Medline]

Kang KJ, Shibukawa Y, Szerencsei RT & Schnetkamp PP (2005). Substitution of a single residue, Asp575, renders the NCKX2 K⁺-dependent Na⁺/Ca²⁺ exchanger independent of K⁺. J Biol Chem 280, 6834–6839.[Abstract/Free Full Text]

Kimura J, Miyamae S & Noma A (1987). Identification of sodium-calcium exchange current in single ventricular cells of guinea-pig. J Physiol 384, 199–222.[Abstract/Free Full Text]

Kleene SJ (1997). High-gain, low-noise amplification in olfactory transduction. Biophys J 73, 1110–1117.[Abstract/Free Full Text]

Kleene SJ & Gesteland RC (1991). Calcium-activated chloride conductance in frog olfactory cilia. J Neurosci 11, 3624–3629.[Abstract]

Kozlova I, Nilsson H, Phillipson M, Riederer B, Seidler U, Colledge WH & Roomans GM (2005). X-ray microanalysis of airway surface liquid in the mouse. Am J Physiol Lung Cell Mol Physiol 288, L874–L878.[Abstract/Free Full Text]

Kurahashi T & Yau KW (1993). Co-existence of cationic and chloride components in odorant-induced current of vertebrate olfactory receptor cells. Nature 363, 71–74.[CrossRef][Medline]

Lagnado L, Cervetto L & McNaughton PA (1988). Ion transport by the Na-Ca exchange in isolated rod outer segments. Proc Natl Acad Sci U S A 85, 4548–4552.[Abstract/Free Full Text]

Lagnado L, Cervetto L & McNaughton PA (1992). Calcium homeostasis in the outer segments of retinal rods from the tiger salamander. J Physiol 455, 111–142.[Abstract/Free Full Text]

Lamb TD, Matthews HR & Torre V (1986). Incorporation of calcium buffers into salamander retinal rods: a rejection of the calcium hypothesis of phototransduction. J Physiol 372, 315–349.[Abstract/Free Full Text]

Leinders-Zufall T, Greer CA, Shepherd GM & Zufall F (1998). Imaging odor-induced calcium transients in single olfactory cilia: specificity of activation and role in transduction. J Neurosci 18, 5630–5639.[Abstract/Free Full Text]

Leinders-Zufall T, Rand MN, Shepherd GM, Greer CA & Zufall F (1997). Calcium entry through cyclic nucleotide-gated channels in individual cilia of olfactory receptor cells: spatiotemporal dynamics. J Neurosci 17, 4136–4148.[Abstract/Free Full Text]

Lindemann B (2001). Predicted profiles of ion concentrations in olfactory cilia in the steady state. Biophys J 80, 1712–1721.[Abstract/Free Full Text]

Manzini I & Schild D (2003). Multidrug resistance transporters in the olfactory receptor neurons of Xenopus laevis tadpoles. J Physiol 546, 375–385.[Abstract/Free Full Text]

Matthews HR & Reisert J (2003). Calcium, the two-faced messenger of olfactory transduction and adaptation. Curr Opin Neurobiol 13, 469–475.[CrossRef][Medline]

Nicoll DA, Longoni S & Philipson KD (1990). Molecular cloning and functional expression of the cardiac sarcolemmal Na⁺-Ca²⁺ exchanger. Science 250, 562–565.[Abstract/Free Full Text]

Noe J, Tareilus E, Boekhoff I & Breer H (1997). Sodium/calcium exchanger in rat olfactory neurons. Neurochem Int 30, 523–531.[CrossRef][Medline]

Pyrski M, Koo JH, Polumuri SK, Ruknudin AM, Margolis JW, Schulze DH & Margolis FL (2007). Sodium/calcium exchanger expression in the mouse and rat olfactory systems. J Comp Neurol 501, 944–958.[CrossRef][Medline]

Reilander H, Achilles A, Friedel U, Maul G, Lottspeich F & Cook NJ (1992). Primary structure and functional expression of the Na/Ca,K-exchanger from bovine rod photoreceptors. EMBO J 11, 1689–1695.[Medline]

Reisert J, Bauer PJ, Yau KW & Frings S (2003). The Ca-activated Cl channel and its control in rat olfactory receptor neurons. J Gen Physiol 122, 349–363.[Abstract/Free Full Text]

Reisert J & Matthews HR (1998). Na⁺-dependent Ca²⁺ extrusion governs response recovery in frog olfactory receptor cells. J Gen Physiol 112, 529–535.[Abstract/Free Full Text]

Reisert J & Matthews HR (1999). Adaptation of the odour-induced response in frog olfactory receptor cells. J Physiol 519, 801–813.[Abstract/Free Full Text]

Reisert J & Matthews HR (2001a). Response properties of isolated mouse olfactory receptor cells. J Physiol 530, 113–122.[Abstract/Free Full Text]

Reisert J & Matthews HR (2001b). Responses to prolonged odour stimulation in frog olfactory receptor cells. J Physiol 534, 179–191.[Abstract/Free Full Text]

Reisert J & Matthews HR (2001c). Simultaneous recording of receptor current and intraciliary Ca²⁺ concentration in salamander olfactory receptor cells. J Physiol 535, 637–645.[Abstract/Free Full Text]

Reuter D, Zierold K, Schroder WH & Frings S (1998). A depolarizing chloride current contributes to chemoelectrical transduction in olfactory sensory neurons in situ. J Neurosci 18, 6623–6630.[Abstract/Free Full Text]

Sanchez-Armass S & Blaustein MP (1987). Role of sodium-calcium exchange in regulation of intracellular calcium in nerve terminals. Am J Physiol Cell Physiol 252, C595–C603.[Abstract/Free Full Text]

Schild D & Restrepo D (1998). Transduction mechanisms in vertebrate olfactory receptor cells. Physiol Rev 78, 429–466.[Abstract/Free Full Text]

Schnetkamp PP (2004). The SLC24 Na⁺/Ca²⁺-K⁺ exchanger family: vision and beyond. Pflugers Arch 447, 683–688.[CrossRef][Medline]

Watanabe Y, Koide Y & Kimura J (2006). Topics on the Na⁺/Ca²⁺ exchanger: pharmacological characterization of Na⁺/Ca²⁺ exchanger inhibitors. J Pharmacol Sci 102, 7–16.[CrossRef][Medline]

Zufall F & Munger SD (2001). From odor and pheromone transduction to the organization of the sense of smell. Trends Neurosci 24, 191–193.[CrossRef][Medline]

	Acknowledgements

 
This work was supported by the Wellcome Trust and by a studentship to S.A. from the Fundação para a Ciência e a Tecnologia, Portugal.

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