| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA
2 Burdon Sanderson Cardiac Science Centre, University Laboratory of Physiology, Oxford OX1 3PT, UK
The Na+–HCO3– cotransporter (NBC) is an important sarcolemmal acid extruder in cardiac muscle. The characteristics of NBC expressed functionally in heart are controversial, with reports suggesting electroneutral (NBCn; 1HCO3– : 1Na+; coupling coefficient N= 1) or electrogenic forms of the transporter (NBCe; equivalent to 2HCO3– : 1Na+; N= 2). We have used voltage-clamp and epifluorescence techniques to compare NBC activity in isolated ventricular myocytes from rabbit, rat and guinea pig. Depolarization (by voltage clamp or hyperkalaemia) reversibly increased steady-state pHi while hyperpolarization decreased it, effects seen only in CO2/HCO3–-buffered solutions, and blocked by S0859 (cardiac NBC inhibitor). Species differences in amplitude of these pHi changes were rat > guinea pig 
rabbit. Tonic depolarization (–140 mV to –0 mV) accelerated NBC-mediated pHi recovery from an intracellular acid load. At 0 mV, NBC-mediated outward current at resting pHi was +0.52 ± 0.05 pA pF–1 (rat, n= 5), +0.26 ± 0.05 pA pF–1 (guinea pig, n= 5) and +0.10 ± 0.03 pA pF–1 (rabbit, n= 9), with reversal potentials near –100 mV, consistent with N= 2. The above results indicate a functionally active voltage-sensitive NBCe in these species. Voltage-clamp hyperpolarization negative to the reversal potential for NBCe failed, however, to terminate or reverse NBC-mediated pHi-recovery from an acid load although it was slowed significantly, suggesting electroneutral NBC may also be operational. NBC-mediated pHi recovery was associated with a rise of [Na+]i at a rate 
25% of that mediated via NHE, and consistent with an apparent NBC stoichiometry between N= 1 and N= 2. In conclusion, NBCe in the ventricular myocyte displays considerable functional variation among the three species tested (greatest in rat, least in rabbit) and may coexist with some NBCn activity.
(Received 30 June 2004;
accepted after revision 16 November 2004;
first published online 18 November 2004)
Corresponding author K. W. Spitzer: Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City 84112, USA. Email: spitzer{at}cvrti.utah.edu
This article has been cited by other articles:
|
|
 |
|
  E. Boedtkjer, J. Praetorius, E.-M. Fuchtbauer, and C. Aalkjaer Antibody-independent localization of the electroneutral Na+-HCO3- cotransporter NBCn1 (slc4a7) in mice Am J Physiol Cell Physiol, February 1, 2008; 294(2): C591 - C603. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Yamamoto, T. Shirayama, T. Sakatani, T. Takahashi, H. Tanaka, T. Takamatsu, K. W. Spitzer, and H. Matsubara Enhanced activity of ventricular Na+-HCO3 cotransport in pressure overload hypertrophy Am J Physiol Heart Circ Physiol, August 1, 2007; 293(2): H1254 - H1264. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. A. Niederer and N. P. Smith A Mathematical Model of the Slow Force Response to Stretch in Rat Ventricular Myocytes Biophys. J., June 1, 2007; 92(11): 4030 - 4044. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Swietach, A. Rossini, K. W. Spitzer, and R. D. Vaughan-Jones H+ Ion Activation and Inactivation of the Ventricular Gap Junction: A Basis for Spatial Regulation of Intracellular pH Circ. Res., April 13, 2007; 100(7): 1045 - 1054. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. C. Villa-Abrille, M. G. V. Petroff, and E. A. Aiello The electrogenic Na+/HCO3- cotransport modulates resting membrane potential and action potential duration in cat ventricular myocytes J. Physiol., February 1, 2007; 578(3): 819 - 829. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Swietach, K. W. Spitzer, and R. D. Vaughan-Jones pH-Dependence of Extrinsic and Intrinsic H+-Ion Mobility in the Rat Ventricular Myocyte, Investigated Using Flash Photolysis of a Caged-H+ Compound Biophys. J., January 15, 2007; 92(2): 641 - 653. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Yamaguchi and T. Ishikawa Electrophysiological characterization of native Na+-HCO3- cotransporter current in bovine parotid acinar cells J. Physiol., October 1, 2005; 568(1): 181 - 197. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
