title: Cellular actions of cAMP on HCO3(-)-secreting cells of rabbit CCD: dependence on in vivo acid-base status.
abstract: HCO3- secretion by cortical collecting duct (CCD) occurs via beta-intercalated cells. In vitro CCD HCO3- secretion is modulated by both the in vivo acid-base status of the animal and by adenosine 3',5'-cyclic monophosphate (cAMP). To investigate the mechanism of cAMP-induced HCO3- secretion, we measured intracellular pH (pHi) of individual beta-intercalated cells of CCDs dissected from alkali-loaded rabbits perfused in vitro. beta-Intercalated cells were identified by demonstrating the presence of an apical anion exchanger (cell alkalinization in response to removal of lumen Cl-). After 180 min of perfusion to permit decrease of endogenous cAMP, acute addition of 0.1 mM 8-bromo-cAMP or 1 microM isoproterenol to the bath caused a transient cellular alkalinization (> 0.20 pH units). In the symmetrical absence of either Na+, HCO3-, or Cl-, cAMP produced no change in pHi. Basolateral dihydrogen 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.1 mM) for 15 min before cAMP addition also prevented this alkalinization. In contrast to the response of cells from alkali-loaded rabbits, addition of basolateral cAMP to CCDs dissected from normal rabbits resulted in an acidification of beta-intercalated cells (approximately 0.20 pH units). The present studies demonstrate the importance of the in vivo acid-base status of the animal in the regulation of CCD HCO3- secretion by beta-intercalated cells. The results identify the possible existence of a previously unrecognized Na(+)-dependent Cl-/HCO3- exchanger on the basolateral membrane of beta-intercalated cells in alkali-loaded rabbits.
authors.affiliation: Department of Medicine, West Los Angeles Veterans Affairs Medical Center, California.
authors.forename: C
authors.initials: C
authors.lastname: Emmons
authors.forename: J B
authors.initials: JB
authors.lastname: Stokes
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000136:Acid-Base Equilibrium; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D007545:Isoproterenol / Q000494:pharmacology; D007672:Kidney Cortex; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D011817:Rabbits; D012016:Reference Values
chemical_list: D001639:Bicarbonates; D000242:Cyclic AMP; D007545:Isoproterenol; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid