Sodium bicarbonate cotransport current in the configuration of cardiac action potential

AIELLO EA; AIELLO EA

Brisbane, Australia

Simposio; XVII World Congress of the International Society for Heart Research (ISHR); 2004

 The Na+/HCO3- cotransport (NBC) contributes to 40-50% of total acid extrusion in ventricular myocardium. There are at least two electrogenic isoforms of the NBC in the heart, NBC1 and NBC4. Measuring Na+-dependent bicarbonate-sensitive currents with perforated-patch we were able to demonstrate the existence in the heart of an electrogenic NBC with a HCO3-:Na+ stoichiometry ratio of 2:1. This electrogenic NBC produces an anionic current which is outward (hyperpolarizing and repolarizing current) at potentials positive to the reversal potential of the NBC. Since the determined reversal potential for this electrogenic NBC is close to –95 mV, when the myocytes are exposed to a solution containing a physiological concentration of bicarbonate a hyperpolarization of resting membrane potential together with a shortening of action potential duration are observed. Thus, the electrogenic NBC participates in the configuration of the cardiac action potential, being this effect usually masked by the wide use of non-bicarbonate solution in electrophysiological recordings. The role of NBC in ischemic-reperfusion injury, heart failure and generation of arrhythmias remains to be determined. However, there is increasing evidence that involves this transporter as one of the Na+-loading mechanisms during reperfusion.