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J Physiol Volume 578, Number 3, 819-829, February 1, 2007 DOI: 10.1113/jphysiol.2006.120170
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CARDIOVASCULAR

The electrogenic Na+/HCO3– cotransport modulates resting membrane potential and action potential duration in cat ventricular myocytes

María C. Villa-Abrille1, Martín G. Vila Petroff1 and Ernesto A. Aiello1

1 Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata 1900, Argentina

Perforated whole-cell configuration of patch clamp was used to determine the contribution of the electrogenic Na+/HCO3– cotransport (NBC) on the shape of the action potential in cat ventricular myocytes. Switching from Hepes to HCO3– buffer at constant extracellular pH (pHo) hyperpolarized resting membrane potential (RMP) by 2.67 ± 0.42 mV (n = 9, P < 0.05). The duration of action potential measured at 50% of repolarization time (APD50) was 35.8 ± 6.8% shorter in the presence of HCO3– than in its absence (n = 9, P < 0.05). The anion blocker SITS prevented and reversed the HCO3–-induced hyperpolarization and shortening of APD. In addition, no HCO3–-induced hyperpolarization and APD shortening was observed in the absence of extracellular Na+. Quasi-steady-state currents were evoked by 8 s duration voltage-clamped ramps ranging from –130 to +30 mV. A novel component of SITS-sensitive current was observed in the presence of HCO3–. The HCO3–-sensitive current reversed at –87 ± 5 mV (n = 7), a value close to the expected reversal potential of an electrogenic Na+/HCO3– cotransport with a HCO3–:Na+ stoichiometry ratio of 2: 1. The above results allow us to conclude that the cardiac electrogenic Na+/HCO3– cotransport has a relevant influence on RMP and APD of cat ventricular cells.

(Received 30 August 2006; accepted after revision 27 November 2006; first published online 30 November 2006)
Corresponding author E. A. Aiello: Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, 60 y 120, La Plata 1900, Argentina.  Email: aaiello{at}atlas.med.unlp.edu.ar






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