ROLES OF CA2+ AND PKC IN REGULATION OF ACID BASE TRANSPORT IN ISOLATED PROXIMAL TUBULES/

Roles of Ca2+ and protein kinase C (PKC) in the regulation of acid/bas e transport in isolated rabbit proximal tubules were investigated by m easuring cytosolic Ca2+ concentrations ([Ca2+](i)) and cell pH (pH(i)) with fluorescent probes. Ionomycin (0.2 mu M) increased [Ca2+](i) by similar to 200 nM but did not affect the basolateral Na+-HCO3- cotrans porter. However, the apical Na+/H+ exchanger was inhibited by 50% by i onomycin, and this inhibition was abolished either by ,2-bis(2-aminoph enoxy)ethane-N,N,N',N'-tetraacetic acid, an intracellular Ca2+ chelato r, or by KN-62, an inhibitor of calcium-calmodulin-dependent protein k inase II (CaM kinase II). On the other hand, phorbol 12-myristate 13-a cetate (PMA, 0.5 mu M) did not affect the apical Na+/H+ exchanger but did stimulate the basolateral Na+-HCO3- cotransporter by 60-80%, and t his stimulation was prevented by calphostin C, an inhibitor of PKC. Co nsistent with the cotransporter stimulation, PMA decreased steady-stat e pH(i) in the presence of CO2/ HCO,. These results indicate that 1) t he acute increase in [Ca2+](i) within physiological ranges inhibits th e apical Na+/H+ exchanger, probably through mediation of CaM kinase II ; and 2) the short-term PKC activation stimulates the basolateral Na+- HCO3- cotransporter.