Sulphates and phosphates reduce the sensitivity to hydrochlorothiazide (HCTZ) of the transepithelial NaCl transport in rabbit gallbladder

The transepithelial fluid transport present in rabbit gallbladder was measured gravimetrically every 30 min or electrically every 6 min; the equivalent isosmotic NaCl transport was then calculated from these measurements. A dose/response curve of the transport upon treatment with HCTZ was obtained gravimetrically, knowing that the apical neutral entry of NaCl into the cell is sustained by a HCTZ sensitive Na+ -Cl- symport. Although the low temporal resolution of this technique and the homeostatic activation of a Na+ -K+-2C1- cotransport (when the Na+ -Cl- symport was inhibited) only allowed to obtain an approximate curve, the inhibition seemed to be maximal only with a HCTZ concentration (10-3 M) tenfold higher than the one correspondingly effective on the same symport in other epithelia. The use of the electrical technique, which allows to measure correctly the inhibition before the appearance of homeostatic reactions, and the elimination of sulphates and phosphates from the bathing salines permitted to observe that also in rabbit gallbladder a 10-4 M HCTZ concentration nearly abolishes the transport.