Effects of dopamine on the transport of Na, H, and Ca in the bullfrog proximal tubule.
To study effects of dopamine (DA, 10(-6) M) 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(-4) M). 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 1.4 mM. 2) DA produced a delayed fall of (Ca)i by 8 nM. 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 pHi 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.
Hagiwara
N
N
Department of Physiology, Osaka Medical College, Japan.
Kubota
T
T
Kubokawa
M
M
Fujimoto
M
M
D000262:Adenylyl Cyclases / Q000502:physiology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D004298:Dopamine / Q000502:physiology*; D004594:Electrophysiology; D006859:Hydrogen / Q000493:pharmacokinetics*; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008839:Microelectrodes; D011892:Rana catesbeiana / Q000502:physiology*; D012964:Sodium / Q000493:pharmacokinetics*
D003994:Bucladesine; D006859:Hydrogen; D012964:Sodium; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium; D004298:Dopamine