Isoproterenol stimulates Cl- current by a Gs protein-mediated process in beta-intercalated cells isolated from rabbit...

To examine the effect of isoproterenol on Cl- current and its signal transduction pathway in beta-intercalated cells (beta-IC cell), peanut agglutinin (PNA) positive cells in culture were studied by the whole-cell 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-clamp mode induced an activation of Cl- current in a dose-dependent fashion and its threshold concentration was in the order of 0.01 microM and ED50 was about 0.1 microM. 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 application of GTP gamma S 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 signal transduction system involving G-protein, adenylate cyclase, cAMP, and protein kinase A.