Electrogenic bicarbonate secretion by guinea pig gallbladder epithelium: apical membrane exit.
Guinea pig gallbladder epithelium secretes HCO3- by electroneutral mechanisms, resulting in transepithelial Cl- -HCO3- exchange. Adenosine 3',5'-cyclic monophosphate (cAMP) converts HCO3- secretion into an electrogenic process. This transformation was examined using voltage-clamp, pH-stat, and microelectrode techniques. Prostaglandin E1 (PGE1; 10(-6) M) was used to raise intracellular cAMP levels. It increased short-circuit current (Isc) by approximately 1.8 mumol.cm-2.h-1, an effect dependent on serosal HCO3- and, partly, on mucosal Cl-. Mucosal 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS; 10(-3) M) halved Isc, but only in Cl- containing solutions. PGE1 increased the secretory HCO3- flux from approximately 2.0 to approximately 2.7 mumol.cm-2.h-1 and reduced the absorptive HCO3- flux from approximately 1.1 to approximately 0.5 mumol.cm-2.h-1, with net HCO3- secretion accounting for the increase in Isc. During single-cell impalements, PGE1 depolarized the apical membrane by greater than 10 mV (transiently in the absence of HCO3-) and decreased the apparent ratio of membrane resistances (Ra/Rb) from 5-8 to a value close to zero. These effects were largely reduced in magnitude and rapidity by removing Cl- and HCO3- from both sides of the epithelium. Ion substitutions in the luminal perfusate revealed substantial Cl- and HCO3- permeabilities at the apical membrane under PGE1 conditions. Our results indicate that, in the presence of PGE1 (cAMP), HCO3- crosses the apical membrane by two different routes. A SITS-sensitive fraction leaves the cell in exchange for luminal Cl-, which, in turn, recycles into the lumen by electrodiffusion. The remaining HCO3- exits through a HCO3- conductive pathway.
Stewart
C P
CP
Abteilung Pharmakologie, Medizinischen Fakultät, Rheinisch-Westfälische Technische Hochschule Aachen, Federal Republic of Germany.
Winterhager
J M
JM
Heintze
K
K
Petersen
K U
KU
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000527:Alprostadil / Q000494:pharmacology; D000818:Animals; D000838:Anions; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D004563:Electrochemistry; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005704:Gallbladder / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects
D000838:Anions; D001639:Bicarbonates; D002712:Chlorides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000242:Cyclic AMP; D000527:Alprostadil; D015056:1-Methyl-3-isobutylxanthine