BETA-ADRENERGIC REGULATION OF H+ SECRETION BY CULTURED OUTER MEDULLARY COLLECTING DUCT CELLS

The effects of the beta-adrenergic agonist isoproterenol (Iso) on cells of the inner stripe portion of the rabbit outer medullary collecting duct (OMCD(i)) grown in primary culture were examined using whole cell patch-clamp techniques and measurements of intracellular pH (pH(i)) and Ca2+. Iso (10(-6) M) increased the cellular Cl- conductance, and this effect was mimicked by treatment of the cells with dibutyryladenosine 3',5'-cyclic monophosphate (cAMP, 10(-5) M) or protein kinase A (PKA, 0.4 U/ml). Iso did not alter the baseline pH(i), but it did increase the activity of both the Cl-/HCO3- antiporter and the H+-adenosinetriphosphatase (H+-ATPase). The increase in Cl-/HCO3- antiporter rate was mimicked by dibutyryl-cAMP plus 3-isobutyl-1-methylxanthine (cAMP + IBMX, 10(-4) M + 10(-5) M). However, the Iso-induced stimulation of the H+-ATPase activity was not mimicked by cAMP + IBMX. Measurements of intracellular Ca2+ showed that Iso also increased intracellular Ca2+ levels. This response was not dependent on extracellular Ca2+, nor did cAMP + IBMX appreciably alter intracellular Ca2+. Consequently, we postulate that beta-adrenergic agonists are potential stimulators of OMCD(i) H+ secretion. These agonists stimulate cellular HCO3- efflux through a signal transduction pathway involving cAMP and PKA. However, a different signal transduction pathway appears to mediate the stimulation of cellular H+ efflux. This second pathway may involve an elevation of intracellular Ca2+.