Abstract
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 (pH(o)) 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.
Highlights
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
It seems unlikely that the changes in AP duration (APD) detected in the presence of HCO S were due to beat-to-beat APD variability
This concentration of IICO3 induced an APD50 and APD90 shortening of 19.3 ±4.6% and 11.9 ±3.8% (n = 9) of the values in the absence of HCO3_, respectively, values that are lower than those observed with 20 mM IICO3 (Fig. 2B). These results demonstrate that the magnitude of the APD shortening observed in HCO3_ is dependent on the extracellular concentration of HCO S
Summary
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. Boulpaep (1983) in the renal proximal tubule of the salamander, with a HCOi /Na stoichiometry of 3:1, which generates a net flux of negative charge across the cell membrane. In the heart, this mechanism was first reported to be present in sheep Purkinje fibres In this study we present evidence for the presence of an electrogenic NBC in isolated cat ventricular myocytes, and for its contribution to the modulation of resting membrane potential (RMP) and AP duration (APD)
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