Protein kinase C-mediated regulation of the renal Na+/dicarboxylate cotransporter, NaDC-1

The Na+/dicarboxylate cotransporter of the renal proximal tubule, NaDC-1, r eabsorbs Krebs cycle intermediates, such as succinate and citrate, from the tubular filtrate. Although long-term regulation of this transporter by chr onic metabolic acidosis and K+ deficiency is well documented, there is no i nformation on acute regulation of NaDC-1. In the present study, the transpo rt of succinate in Xenopus oocytes expressing NaDC-1 was inhibited up to 95 % by two activators of protein kinase C, phorbol 12-myristate, 13-acetate ( PMA) and sn-1,2-dioctanoylglycerol (DOG). Activation of protein kinase A ha d no effect on NaDC-1 activity. The inhibition of NaDC-1 transport by PMA w as dose-dependent, and could be prevented by incubation of the oocytes with staurosporine. Mutations of the two consensus protein kinase C phosphoryla tion sites in NaDC-1 did not affect inhibition by PMA. The inhibitory effec ts of PMA were partially prevented by cytochalasin D, which disrupts microf ilaments and endocytosis. PMA treatment was also associated with a decrease of approximately 30% in the amount of NaDC-1 protein found on the plasma m embrane. We conclude that the inhibition of NaDC-1 transport activity by PM A occurs by a combination of endocytosis and inhibition of transport activi ty. (C) 1999 Elsevier Science B.V. All rights reserved.