The nature of the neutral Na+−Cl−-coupled entry at the apical membrane of rabbit gallbladder epithelium: II. Na+−Cl− symport is independent of K+

Abstract

In the epithelium of rabbit gallbladder, in the nominal absence of bicarbonate, intracellular Cl- activity is about 25 mM, about 4 times higher than intracellular Cl- activity at the electrochemical equilibrium. It is essentially not affected by 10(-4) M acetazolamide and 10(-4) M 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS) even during prolonged exposures: it falls to the equilibrium value by removal of Na+ from the lumen without significant changes of the apical membrane potential difference. Both intracellular Cl- and Na+ activities are decreased by luminal treatment with 25 mM SCN-; the initial rates of change are not significantly different. In addition, the initial rates of change of intracellular Cl- activity are not significantly different upon Na+ or Cl- entry block by the appropriate reduction of the concentration of either ion in the luminal solution. Luminal K+ removal or 10(-5) M bumetanide do not affect intracellular Cl- and Na+ activities or Cl- influx through the apical membrane. It is concluded that in the absence of bicarbonate NaCl entry is entirely due to a Na+-Cl- symport on a single carrier which, at least under the conditions tested, does not cotransport K+.

The nature of the neutral Na+−Cl− coupled entry at the apical membrane of rabbit gallbladder epithelium: III. Analysis of transports on membrane vesicles

“…Bumetanide, also in intact rabbit gallbladder, does not modify the unidirectional C1-influx across the apical membrane, or the intracellular activities of Na + and C1- (Cremaschi et al, 1987b). In contrast, in preliminary experiments with HCTZ (5 • 10 .5 M) we observed a significant reduction in the rapid proton dissipation usually observed in the presence of a [Na + ] and [C1-] gradient.…”

Inhibitors of the Cl - /HCO 3 - exchanger activate an apical anion conductance with similar features in the epithelial cells of rabbit gallbladder: analysis in intact epithelium

“…When rabbit gallbladder tissue is incubated with bicarbonate-containing Krebs-Henseleit solution, the measured unidirectional apical Cl -influx is composed of two fractions, related to apical anion exchange and apical Na + -Cl -symport [9,10]. The fraction relating to apical anion exchange has been identified here as the acetazolamide-, SITS-or bicarbonate-sensitive fraction; concentrations, exposure times and protocols used were selected on the basis of kinetics and time courses previously determined [8,10].…”

“…In rabbit gallbladder epithelium a Na + -Cl -symport, which is insensitive to K + and loop diuretics, and a Na + /H + ,Cl -/HCO 3 -double exchange cooperate in promoting a very large apical influx of NaCl into the cell [8,9,10,13,14]. Hydrochlorothiazide (HCTZ) inhibits the apical Na + -Cl -symport as it does with the symport found in kidney distal tubules and flounder urinary bladder [3,16,36,38].…”

“…All the electrophysiological experiments were performed with HCO 3 -/CO 2 -free salines, steadily bubbled with 100% O 2 . Thus the exchanger, though present, was silent or at most working at a lower level, as Cl -/Cl -exchanger [6,8,9,10] and the inhibitors binding to it could not cause cell volume and intracellular pH changes.…”

Purification of proteins of the Na/Cl cotransporter from membranes of Ehrlich ascites cells using a bumetanide-sepharose affinity column

“…Na/K/C1 and Na/C1 cotransport in epithelial cells have been suggested to be functions of the same pathway, interconvertible depending on cell volume (Eveloff & Calamia, 1986;Eveloff & Warnock, 1987). However, the importance of K-independent Na/C1 cotransport has recently been emphasized (Cremaschi et al, 1987).…”