THE ELECTROGENIC Na+/HCO3- COTRANSPORT MODULATES RESTING MEMBRANE POTENTIAL AND ACTION POTENTIAL DURATION IN CAT VENTRICULAR MYOCYTES.

VILLA-ABRILLE MC; VILA PETROFF MG; AIELLO EA

THE JOURNAL OF PHYSIOLOGY

Cambridge Univ. Press

Lugar: Londres; Año: 2007 vol. 578 p. 819 - 829

0022-3751

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 seconds 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.