HCO3--DEPENDENT ALKALINIZING TRANSPORTER IN ADULT-RAT VENTRICULAR MYOCYTES - CHARACTERIZATION AND MODULATION

The present work was designed to identify the HCO3- dependent alkalini zing carrier in ventricular myocytes of normal and diabetic adult rats and to determine to what extent this system contributes to acid-equiv alent extrusion after an intracellular acidification. We also examined the possible influence of intracellular Ca2+ (Ca2+) and glycolytic in hibition on the carrier activation. Intracellular pH (pH(i)) was recor ded using seminaphthorhodafluor-1. The NH4+ method was used to induce an intracellular acid load. Evidence is provided for the existence of a Cl--independent Na+-HCO3-, cotransport contributing to pH(i) recover y from an intracellular acid load in ventricular cells of adult rats. Na+-HCO3- cotransport accounts for 33% of the total acid-equivalent ef flux (J(H)(e)) from normal adult myocytes after intracellular acidific ation at pH(i) 6.75 in CO2/HCO3--buffered solution. In addition, the a ctivity of this carrier, which is not affected either by decreasing Ca -i(2+) or by inhibiting Ca2+/calmodulin protein kinase II, is downregu lated by inhibition of glycolysis. Under pathophysiological conditions such as diabetes, although total J(H)(e) was significantly decreased compared with normal myocytes, J(H)(e)-carried by Na+-HCO3-, cotranspo rt remained unchanged. However, because of a decrease in Na+/H+ exchan ge, the contribution of this carrier to total J(H)(e) increased with d ecreasing pH(i) (i.e., under conditions that may be associated with an ischemic episode), reaching similar to 58% of total J(H)(e) at pHi 6. 75 (vs. similar to 33% in normal myocytes).