The effects of trimethadione and ethosuximide on ion movement across the toad bladder.

The effects of three drugs, pentylenetetrazol (PTZ), trimethadione (TMO), and ethosuximide on ion movement across the isolated toad urinary bladder as deduced from changes in short current (SCC) were studied, singly and in combination. The effects of the drugs were measured under control conditions (both sides of the bladder bathed by normal Ringer's solution) and experimental conditions (after exposure to a high potassium Ringer's solution, 60mM potassium, and its subsequent replacement by normal Ringer's solution). PTZ enhances the transient increase in bladder SCC is the experimental condition. Ethosuximide produced an increase in SCC when added to the normal Ringer's solution bathing either the mucosal of the serosal surface of the membrane. This response to ethosuximide was different from that to TMO which had not effect on SCC under these conditions. The actions of ethosuximide were attributed to an increase in the mucosal membrane permeability to sodium and stimulation of the sodium pump. TMO and ethosuximide both depressed the SCC response of experimental bladders. TMO and ethosuximide partially blocked the normal response to PTZ. These data suggested that both TMO and ethosuximide decreased the permeability of the serosal membrane to potassium.