PROTEIN-KINASE-C ACTIVATION CAUSES INHIBITION OF NA/K-ATPASE ACTIVITY IN MADIN-DARBY CANINE KIDNEY EPITHELIAL (MDCK) CELLS

To evaluate the influence of protein kinase C (PKC) activation on Na/K-ATPase activity in MDCK cells, we studied the effect of phorbol myristate acetate (PMA) and two diacylglycerol analogues, oleoylacetylglycerol and dioctanoylglycerol, on the enzyme activity. Na/K-ATPase activity was determined by cytochemistry. PMA induced a time- and dose-dependent inhibition of Na/K-ATPase activity and at 100 ng/ml decreased the enzyme activity by 55% of the initial value. These effects were mimicked by oleoylacetylglycerol and dioctanoylglycerol, and were abolished by two inhibitors of PKC, 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H7) and sphingosine. A phorbol ester that does not activate PKC, 4-alpha-phorbol 12,13-didecanoate, did not inhibit Na/K-ATPase activity. PMA inhibition persisted in the presence of cycloheximide and actinomycin D but not in the presence of amiloride. Dopamine (10-mu-M) inhibition of Na/K-ATPase activity was abolished in a dose-dependent manner by sphingosine. Results suggest that in MDCK cells Na/K-ATPase is an effector protein for PKC and that dopamine inhibition of its activity may be mediated by PKC.