The effects of triaminopyrimidine on the short circuit current and transmembrane potentials of the isolated rat visceral yolk sac in vitro.

Intracellular potentials in the cells from 17.5-day old rat visceral yolk sacs were measured by a glass microelectrode. When penetrated from the maternal side, the cells have potentials of about 50.2 +/- 1.9 mV (inside negative) which were reduced by increasing the external K+ concentration and increased by removing Na+ ions from the bathing fluid. Triaminopyrimidine (TAP) which inhibited Na+ transport caused a dose-dependent depolarization of the cell membrane. The depolarization was dependent on the presence of extracellular Ca2+ ions. It is proposed that TAP may inhibit Na+ transport by increasing the intracellular concentration of calcium ions.