Key result
HCO3- buffer shortens ventricular myocyte APD50 by ~36% compared with Hepes buffer.
Why the study?
Does the electrogenic Na+/HCO3- cotransport modulate resting membrane potential and action potential duration in isolated cat ventricular myocytes?
Does the electrogenic Na+/HCO3- cotransport modulate resting membrane potential and action potential duration in isolated cat ventricular myocytes?
The demonstration of an electrogenic Na+/HCO3- cotransport in cat ventricular myocytes that modulates resting membrane potential and action potential duration expands the understanding of basic cardiac electrophysiology in larger mammals.
No immediate clinical implications; extends basic electrophysiology of Na+/HCO3- cotransport in larger mammals but leaves open human relevance.
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.
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Villa‐Abrille et al. (2006) studied this question. HCO3- buffer vs. Hepes buffer was evaluated on Action potential duration at 50% repolarization (APD50) (35.8 ± 6.8% shorter, p=<0.05). Switching from Hepes to HCO3- buffer shortened action potential duration at 50% repolarization by 35.8% and hyperpolarized resting membrane potential by 2.67 mV in cat ventricular myocytes.
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