ISOPROTERENOL STIMULATES CL- CURRENT BY A GS PROTEIN-MEDIATED PROCESSIN BETA-INTERCALATED CELLS ISOLATED FROM RABBIT KIDNEY

To examine the effect of isoproterenol on Cl- current and its signal t ransduction pathway in beta-intercalated cells (beta-IC cell), peanut agglutinin (PNA) positive cells in culture were studied by the whole-c ell clamp technique. We identified these cells as beta-IC cells by PNA -binding, cell alkalinization induced by Cl- free in the superfusate, and an increase in intracellular cAMP concentration by isoproterenol, but not by vasopressin. Application of isoproterenol in the voltage-cl amp mode induced an activation of Cl- current in a dose-dependent fash ion and its threshold concentration was in the order of 0.01 mum and E D50 was about 0. 1 mum. This effect of isoproterenol was inhibited by atenolol, a beta-adrenergic blocker. Either extracellular application of forskolin or intracellular application of cAMP mimicked the action of isoproterenol. In the presence of forskolin or cAMP, isoproterenol caused little further activation of Cl- current. A synthetic inhibitor of protein kinase A (5-24 amide) inhibited the Cl--channel activation by isoproterenol. Isoproterenol failed to activate the current in the presence of intracellular GDP(beta)S. By contrast, intracellular appl ication of GTPgammaS rendered irreversible the Cl--channel activation by brief exposure to isoproterenol. The present studies provide direct evidence that in the PNA-binding cell, probably the beta-IC cell, the stimulation. of beta-adrenoceptor activates Cl- current through the s ignal transduction system involving G-protein, adenylate,cyclase, cAMP , and protein kinase A.