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  • 1
    The 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.
  • 2
    Switching 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).
  • 3
    Quasi-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.
  • 4
    In 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.).
  • 5
    The 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.