DIACYLGLYCEROL ACTIVATION OF PROTEIN-KINASE-C RESULTS IN A DUAL EFFECT ON NA+,K+-ATPASE ACTIVITY FROM INTACT RENAL PROXIMAL TUBULE CELLS

This study evaluated the effect of L-1-oleoyl-2-acetoyl-sn-3-glycerol (OAG) on ouabain-sensitive Na,K-dependent oxygen consumption (Na,K-QO2) in intact renal proximal tubule cells (RPTC). Basal Na,K-QO2 (nmol O2/mg protein per min) was 20.0 +/- 1.0. Incubation with 10 nM of OAG induced a dual effect on Na,K-QO2, with an initial stimulation (maximal at 10 min, 37.1 +/- 5.0), followed by an inhibition (significant at 20 min, 16.3 +/- 1.0). No changes in ouabain-insensitive QO2 were observed in any of the protocols. The effects were abolished by sphingosine, a protein kinase C inhibitor. Stimulation was abolished by amiloride 0.1 mM. Amiloride had no effect on Na,K-QO2 at the concentration used. Stimulation was not potentiated by the sodium ionophore, amphotericine B, and the later inhibition was still observed in the presence of amphotericine B. The initial stimulation was attributed to an increase in sodium permeability, while the later inhibition was attributed to a direct effect on the Na,K-pump. Regulation of Na+,K+-ATPase activity by protein kinase C in intact RPTC can be accomplished by a direct effect on the protein or as a secondary effect consequent upon changes in intracellular sodium.