Protein kinase C activation has dissimilar effects on sodium-coupled uptakes in renal proximal tubular cells in primary culture

Protein kinase C (Ca2+/phospholipid-dependent enzyme) was shown to be present in renal brush border membranes. To evaluate the influence of protein kinase C activation on three apical transport systems, we studied the effect of phorbol myristate acetate (PMA) and of two diacylglycerol analogs, oleoylacetylglycerol and dioctanoylglycerol, on sodium-dependent uptakes of phosphate (Pi), L-alanine, and alpha-methyl-D-glucopyranoside (MGP), as well as on specific phlorizin binding, in cultured rabbit proximal tubular cells. PMA, at 100 ng/ml, decreased the Vmax of Pi and MGP uptake by 30 and 17%, respectively, but not that of alanine uptake. None of the Km values were affected. PMA also decreased the number of phlorizin binding sites by 40%. PMA-induced inhibition of Pi and MGP uptake was time- and concentration-dependent, was mimicked by oleoylacetylglycerol, dioctanoylglycerol, and the diacylglycerol kinase inhibitor R59022, and was reversed by the protein kinase C antagonist 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7). The effects of PMA persisted in the presence of amiloride and dimethyl amiloride, and were potentiated by Ca2+ ionophore A23187. Opening of tight junctions blunted subsequent PMA-induced decrease of MGP uptake, but not of Pi uptake. It is concluded that: (i) activation of protein kinase C does not affect similarly Na-Pi, Na-hexose, and Na-alanine cotransport; and (ii) different pathways are likely to be involved in the observed effects.