Aldosterone Modulates both the Na/H Antiport and Cl/HCO3Exchanger in Cultured Neonatal Rat Cardiac Cells

Mineralocorticoid hormones regulate many physiological functions in the cardiovascular system. Although high affinity binding sites for aldosterone have been found in myocardium, aldosterone effects on pHiregulatory systems in cardiac cells have not been described. We have addressed this issue by using microspectrofluorimetric monitoring of intracellular pH in developing neonatal rat cardiomyocytes cultured for 2 weeks. Developmental changes in cell morphology were controlled by anti-myosin light chain antibody staining of the sarcomeric units using confocal laser scanning microscopy. The data obtained demonstrate that from early stages of the development, pHiin neonatal cardiac cells is regulated by three ion transporting mechanisms, namely, Na/H antiport, Na- and HCO3-dependent transporter and Cl/HCO3exchanger. A 24-h treatment of the cells with aldosterone increases the activity of the Cl/HCO3exchanger at day 6 of cell culture while the Na/H antiport activity is enhanced in the cells treated with the hormone at days 9 and 13 of culture. Thus, by affecting the activity of ionic transporters, aldosterone modulates acid-base balance in cardiac cells.