Effects of isoproterenol on potassium secretion by the cortical collecting tubule

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Abstract
These studies tested the effects of isoproterenol on potassium secretion in the isolated perfused cortical collecting tubule. Isoproterenol, 10(-6) M (n = 6) and 10(-4) M (n = 2), added to bathing solution produced a significant fall in potassium secretion [13.5 +/- 1.2 to 8.0 +/- 0.9 peq X mm-1 X min-1 (P less than 0.01)] and in transepithelial voltage (P less than 0.01) compared with time controls (n = 9). Pretreatment with propranolol abolished this effect (n = 4). Addition of propranolol alone to the bath caused no significant change in potassium secretion (n = 8). 8-[p-Chlorophenylthio]cAMP (10(-4) M, isotonic perfusate) added to the bath produced a significant fall in potassium secretion [11.5 +/- 1.7 to 7.2 +/- 1.3 peq X mm-1 X min-1, n = 7 (P less than 0.01)]. Arginine vasopressin (25 microU/ml), which also stimulates adenylate cyclase activity in this segment, had no significant effect on potassium secretion (n = 10). When chloride was replaced by methyl sulfate in all solutions (n = 6), there was a significant attenuation in the fall in potassium secretion in experiments with 10(-6) M isoproterenol compared with experiments with chloride-containing bath solutions (P less than 0.05). These data suggest that isoproterenol has a specific action of reducing potassium secretion in the cortical collecting tubule either through alternating chloride transport per se or through some other effect dependent on the presence of chloride (e.g., hydrogen ion secretion). Also, this effect is probably mediated by cAMP-dependent events. The lack of effect of vasopressin on potassium secretion suggests that separate cells or cellular pools of cAMP are involved in hormonal stimulation by isoproterenol and vasopressin in this nephron segment.