THE EFFECT OF A BENZOTHIADIAZIDE ON THE ISOLATED TOAD BLADDER

¹ Departments of Physiology and Pharmacology, University of Kansas Medical Center, Kansas City, Kansas

Application of bendroflumethiazide (BHFT) to the serosal surface of the isolated toad bladder promptly reduced short-circuit current (SCC) and conductance and later reduced the transepitheial potential difference. This effect can be reversed by removal of the drug. BHFT depressed the SCC largely by reducing the Na flux from the mucosal to the serosal medium. In control experiments there is a direct correlation between tissue conductance and the passive back flux of Na from serosa to mucosa. Despite the effect of BHFT on conductance, the drug did not consistently affect this flux. Mucosal application of BHFT stimulated SCC and potential difference. The effect of BHFT and that of antidiuretic hormone on SCC were additive. BHFT did not affect water flow or potentiate this effect of antidiuretic hormone. Exposure of both surfaces of the bladder to BHFT transiently stimulated SCC and then depressed it. BHFT entered the tissue from the serosal medium but did not cross into the mucosal medium. The drug did not enter the tissue when it was placed in the mucosal medium. BHFT did not affect tissue potassium concentrations.