Evidence for an electrogenic Na+-HCO3− symport in rat cardiac myocytes
Article first published online: 22 SEP 2004
The Journal of Physiology
Volume 512, Issue 1, pages 137–148, October 1998
How to Cite
Aiello, E. A., Petroff, M. G. V., Mattiazzi, A. R. and Cingolani, H. E. (1998), Evidence for an electrogenic Na+-HCO3− symport in rat cardiac myocytes. The Journal of Physiology, 512: 137–148. doi: 10.1111/j.1469-7793.1998.137bf.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- (Received 24 March 1998; accepted after revision 26 June 1998.)
- 1The perforated whole-cell configuration of patch clamp and the pH fluorescent indicator SNARF were used to determine the electrogenicity of the Na+-HCO3− cotransport in isolated rat ventricular myocytes.
- 2Switching from Hepes buffer to HCO3− buffer at constant extracellular pH (pHo) hyperpolarized the resting membrane potential (RMP) by 2.9 ± 0.4 mV (n= 9, P < 0.05). In the presence of HCO3−, the anion blocker SITS depolarized RMP by 2.6 ± 0.5 mV (n= 5, P < 0.05). No HCO3−-induced hyperpolarization was observed in the absence of extracellular Na+. The duration of the action potential measured at 50 % of repolarization time (APD50) was 29.2 ± 6.1 % shorter in the presence of HCO3− than in its absence (n= 6, P < 0.05).
- 3Quasi-steady-state currents were evoked by voltage-clamped ramps ranging from −130 to +30 mV, during 8 s. The development of a novel component of Na+-dependent and Cl−-independent steady-state outward current was observed in the presence of HCO3−. The reversal potential (Erev) of the Na+-HCO3− cotransport current (INa,Bic) was measured at four different levels of extracellular Na+. A HCO3−:Na+ ratio compatible with a stoichiometry of 2:1 was detected. INa,Bic was also studied in isolation in standard whole-cell experiments. Under these conditions, INa,Bic reversed at −96.4 ± 1.9 mV (n= 5), being consistent with the influx of 2 HCO3− ions per Na+ ion through the Na+-HCO3− cotransporter.
- 4In the presence of external HCO3−, after 10 min of depolarizing the membrane potential (Em) with 45 mm extracellular K+, a significant intracellular alkalinization was detected (0.09 ± 0.03 pH units; n= 5, P < 0.05). No changes in pHi were observed when the myocytes were pre-treated with the anion blocker DIDS (0.001 ± 0.024 pH units; n= 5, n.s.), or when exposed to Na+-free solutions (0.003 ± 0.037 pH units; n= 6, n.s.).
- 5The above results allow us to conclude that the cardiac Na+-HCO3− cotransport is electrogenic and has an influence on RMP and APD of rat ventricular cells.