Role of the calcium/calmodulin-dependent protein kinase II in the regulation of the renal basolateral PAH and dicarboxylate transporters

The aim of the present study was to investigate whether the activities of t he renal basolateral organic anion transporter (PAH transporter) and the so dium-dependent dicarboxylate transporter are modulated by the calcium/calmo dulin-dependent multifunctional protein kinase II (CaM kinase II). The stud ies were performed on isolated S-2 segments of proximal tubules microdissec ted from rabbit kidneys without the use of enzymatic agents. H-3-PAH was us ed as marker substance of the anion transporter, and C-14-glutarate as a ma rker of the sodium/dicarboxylate cotransporter. Because the tubules were no t perfused, and hence were collapsed, the tubular uptake of the marker subs tances reflects transport across the basolateral cell membrane. To obtain u ptake rates most closely related to initial transport rates, 30 s tubular u ptake measurements were performed. The results show that a selective inhibi tor of CaM kinase II, KN93, inhibited tubular PAH uptake. The smallest effe ctive dose was 10(-7) M. An inactive analogue of KN93, KN92, was without ef fect, even at the high concentration of 10(-5) M. In contrast to PAH, trans port, tubular C-14-glutarate uptake was not affected by KN93 (10(-5) M). PA H transport was also inhibited after elevation of intracellular Ca2+ by the Ca2+-ionophore: A 23187 and by the polycationic antibiotic neomycin, but n ot by the intracellular Ca2+ modulators thapsigargin and ryanodine. The eff ect of the Ca2+-ionophore could be abolished by KN93, but not by Rp-cAMP(s) , an inhibitor of protein kinase A, indicating that this event was mediated by CaM kinase II, but not by PKA. The results provide the first evidence t hat, in addition to the protein kinases A and C (previous studies from this lab), CaM kinase II has a role in the regulation of the renal basolateral PAH transporter, whereas the renal basolateral dicarboxylate transporter do es not depend on CaM kinase II activity. (C) Elsevier, Paris.