HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Selyanko, A. A. Articles by Sim, J. A. Search for Related Content PubMed PubMed Citation Articles by Selyanko, A. A. Articles by Sim, J. A.

Ca²⁺-inhibited non-inactivating K⁺ channels in cultured rat hippocampal pyramidal neurones

A. A. Selyanko and J. A. Sim

1. Whole-cell perforated-patch recording from cultured CA1-CA3 pyramidal neurones from neonatal rat hippocampus (20-22 °C; [K⁺]_o = 2·5 mM) revealed two previously recorded non-inactivating (sustained) K⁺ outward currents: a voltage-independent 'leak' current (I_leak) operating at all negative potentials, and, at potentials -60 mV, a time- and voltage-dependent 'M-current' (I_K(M)). Both were inhibited by 1 mM Ba²⁺ or 10 µM oxotremorine-M (Oxo-M). In ruptured-patch recording using Ca²⁺-free pipette solution, I_leak was strongly enhanced, and was inhibited by 1 mM Ba²⁺ but unaffected by 0·5 mM 4-aminopyridine (4-AP), 1 mM tetraethylammonium (TEA) or 1-10 nM margatoxin.

2. Single channels underlying these currents were sought in cell-attached patch recordings. A single class of channels of conductance ~7 pS showing sustained activity at resting potential and above was identified. These normally had a very low open probability (P_o < 0·1), which, however, showed a dramatic and reversible increase (to about 0·9 at ~0 mV) following the removal of Ca²⁺ from the bath. Under these (Ca²⁺-free) conditions, single-channel P_o showed both voltage-dependent and voltage-independent components on patch depolarization from resting potential. The mean activation curve was fitted by a modified Boltzmann equation. When tested, all channels were reversibly inhibited by addition of 10 µM Oxo-M to the bath solution.

3. The channels maintained their high P_o in patches excised in inside-out mode into a Ca²⁺-free internal solution and were strongly inhibited by application of Ca²⁺ to the inner face of the membrane (IC₅₀ = 122 nM); this inhibition was observed in the absence of MgATP, and therefore was direct and unrelated to channel phosphorylation/dephosphorylation.

4. Channels in patches excised in outside-out mode were blocked by 1 mM Ba²⁺ but were unaffected by 4-AP or TEA.

5. Channels in cell-attached patches were inhibited after single spikes, yielding inward ensemble currents lasting several hundred milliseconds. This was prevented in Ca²⁺-free solution, implying that it was due to Ca²⁺ entry.

6. The properties of these channels (block by internal Ca²⁺ and external Oxo-M and Ba²⁺, and the presence of both voltage-dependent and voltage-independent components in their P_o/V relationship) show points of resemblance to those expected for channels associated with both I_leak and I_K(M) components of the sustained macroscopic currents. For this reason we designate them K_sust ('sustained current') channels. Inhibition of these channels by Ca²⁺ entry during an action potential may account for some forms of Ca²⁺-dependent after-depolarization. Their high sensitivity to internal Ca²⁺ may provide a new, positive feedback mechanism for cell excitation operating at low (near-resting) [Ca²⁺]_i.

This article has been cited by other articles:

				S. Chen and Y. Yaari Spike Ca2+ influx upmodulates the spike afterdepolarization and bursting via intracellular inhibition of KV7/M channels J. Physiol., March 1, 2008; 586(5): 1351 - 1363. [Abstract] [Full Text] [PDF]

				S. Piccinin, A. D. Randall, and J. T. Brown KCNQ/Kv7 Channel Regulation of Hippocampal Gamma-Frequency Firing in the Absence of Synaptic Transmission J Neurophysiol, May 1, 2006; 95(5): 3105 - 3112. [Abstract] [Full Text] [PDF]

				X. Chen and D. Johnston Properties of single voltage-dependent K+ channels in dendrites of CA1 pyramidal neurones of rat hippocampus J. Physiol., August 15, 2004; 559(1): 187 - 203. [Abstract] [Full Text] [PDF]

				P. Roper, J. Callaway, and W. Armstrong Burst Initiation and Termination in Phasic Vasopressin Cells of the Rat Supraoptic Nucleus: A Combined Mathematical, Electrical, and Calcium Fluorescence Study J. Neurosci., May 19, 2004; 24(20): 4818 - 4831. [Abstract] [Full Text] [PDF]

				M. Schwake, M. Pusch, T. Kharkovets, and T. J. Jentsch Surface Expression and Single Channel Properties of KCNQ2/KCNQ3, M-type K+ Channels Involved in Epilepsy J. Biol. Chem., April 28, 2000; 275(18): 13343 - 13348. [Abstract] [Full Text] [PDF]