ALDOSTERONE MODULATES BOTH THE NA H ANTIPORT AND CL/HCO3 EXCHANGER INCULTURED NEONATAL RAT CARDIAC-CELLS/

Mineralocorticoid hormones regulate many physiological functions in th e cardiovascular system. Although high affinity binding sites for aldo sterone have been found in myocardium, aldosterone effects on pH(i) re gulatory systems in cardiac cells have not been described. We have add ressed this issue by using microspectrofluorimetric monitoring of intr acellular pH in developing neonatal rat cardiomyocytes cultured for 2 weeks. Developmental changes in cell morphology were controlled by ant i-myosin light chain antibody staining of the sarcomeric units using c onfocal laser scanning microscopy. The data obtained demonstrate that from early stages of the development, pH(i) in neonatal cardiac cells is regulated by three ion transporting mechanisms, namely, Na/H antipo rt, Na- and HCO3-dependent transporter and Cl/HCO3 exchanger. A 24-h t reatment of the cells with aldosterone increases the activity of the C l/HCO3 exchanger at day 6 of cell culture while the Na/H antiport acti vity is enhanced in the cells treated with the hormone at days 9 and 1 3 of culture. Thus, by affecting the activity of ionic transporters, a ldosterone modulates acid-base balance in cardiac cells. (C) 1995 Acad emic Press Limited