Na(+)-H+ exchange is stimulated by protein kinase C activation in inner medullary collecting duct cells

Abstract

In this study we investigated the role of protein kinases in activation of the Na(+)-H+ exchanger in inner medullary collecting duct (IMCD) cells. Monolayers, 24-48 h after achieving confluence, were made quiescent by 24 h incubation in 0.1% serum before study. Changes in pHi were measured with 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Phorbol myristate acetate (PMA), a synthetic analogue of diacylglycerol (DAG), was used to stimulate protein kinase C (PKC). In nominally HCO3(-)-free media containing 110 mM Na+ and 1 mM Ca2+, PMA addition increased pHi from 7.29 +/- 0.08 to 7.54 +/- 0.07 after 20 min. The increment in pHi was completely inhibited by 1 mM amiloride or by replacement of extracellular Na+ with choline but not inhibited by 1 mM N-ethylmaleimide, an inhibitor of active proton transport. Downregulation of PKC by overnight incubation of monolayers with PMA also prevented the rise in pHi upon subsequent challenge with PMA. Another active analogue of DAG, 1,2-dioleoyl-rac-glycerol, caused an increment in pHi similar to that produced by PMA, whereas 4 alpha-phorbol, an inactive analogue, did not stimulate Na(+)-H+ exchange. Bradykinin (10(-6) M), a phospholipase C-activating hormone, also induces alkalinization of IMCD cells similar to that produced by phorbol esters. Neither vasopressin (10(-7) M), which induces cellular accumulation of adenosine 3',5'-cyclic monophosphate (cAMP) and activation of protein kinase A (PKA), nor 8-bromo-cAMP (1 mM) changed pHi. Therefore in the IMCD cell activation of PKC but not PKA stimulates a rise in pHi via the Na(+)-H+ exchanger.