Role of the electrogenic Na+/HCO3- symport in the heart

The Na+/HCO3- cotransport (NBC) contributes to 40-50% of total acid extrusion in ventricular myocardium. There is, at least, one electrogenic isoform of the NBC in the heart, with a stoichiometry ratio of 2HCO(3)(-): 1Na(+). This cardiac electrogenic NBC abbreviates the action potential and hyperpolarizes the resting membrane potential, being these effects usually masked by the wide use of non-bicarbonate solutions in the electrophysiological recordings. The activation of the electrogenic NBC atkalinazes the cell after increases in heart rate, suggesting a role of this transporter in the compensation for the enhanced proton production induced by the acceleration of cell metabolism. The role of NBC in ischemic-reperfusion injury and heart failure remains to be determined. However, there is increasing evidence that involves this transporter as one of the Na+-Joading mechanisms during reperfusion.