EFFECTS OF DOPAMINE ON THE TRANSPORT OF NA, H, AND CA IN THE BULLFROG PROXIMAL TUBULE

To study effects of dopamine (DA, 10-6M) on ion transport processes in proximal tubular cells, we used Na+-, H+-, and Ca2+-selective microelectrodes in doubly-perfused bullfrog kidneys. The peritubular membrane potential difference (EM) and cytosolic Na+, Ca2+, and H+ activities ((Na)i, (Ca)i, and pHi) were measured continuously after peritubular administration of DA or dibutyryl-cyclic AMP (db-cAMP, 10-4M). Results obtained are as follows. 1) DA induced a decrease of (Na)i by 4.2 mM, but during the luminal perfusion of 0.5 mM Na+ solution, DA decreased (Na)i only by 1.4mM. 2) DA produced a delayed fall of (Ca); by 8nM. 3) DA produced hyperpolarization of EM by 5-7 mV. 4) Peritubular perfusion with high K+ (35 mM) solution produced about 30 mV depolarization of EM. DA added to high K+ perfusate induced 38 mV depolarization. 5) DA increased pHs by 0.07. 6) DA produced almost the same changes in (Na)i, (Ca)i, EM, and pHi as those induced by db-cAMP. 7) Effects of DA on EM and (Na)i were inhibited by dopamine1 (DA1) antagonist. Conclusions: Effects of DA on ion transport in the proximal tubular cells are mediated by the adenylate-cyclase-cAMP system. The activation of this system induces 1) suppression of Na+ entry step across the luminal membrane, 2) an increase of K+ permeability in the peritubular membrane, 3) cytosolic alkalinization with vesicular accumulation of H+ by enhancing H+ pump, and 4) a decrease of (Ca)i possibly by restricting Ca2+ entry across the luminal membrane and activating Ca2+ pump in the peritubular membrane or subcellular organelles. © 1990, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.