Abstract

Verapamil decreases the short-circuit current across the toad urinary bladder when present at either the serosal or mucosal surface. The potential difference decreases much less so that the electrical resistance is increased. This indicates a change in ion transfer across the bladder, probably a reduction of Na⁺ movement. The effects of the drug at the mucosal side were overcome by vasopressin and amphotericin B while if present at the serosal surface, neither of these compounds nor cyclic adenosine monophosphate were effective. A 20-fold change in the Ca⁺ concentration of the bathing fluids did not alter the response to the verapamil. Stimulation of short-circuit current by aldosterone did not interfere with verapamil's effect. Verapamil did not inhibit the vasopressin-induced osmotic water transfer across the toad bladder. The oxygen consumption of the toad bladder decreased by 30% in the presence of verapamil but this was not seen in the absence of sodium. The short-circuit current across the toad colon was not affected by the drug but that across the skin was reduced.