Action of amphotericin B on the toad bladder: evidence for sodium transport along two pathways.

1. The relationship of short-circuit current (SCC, sodium transport) and potential difference (p.d.) across the toad bladder to the concentration of sodium on the mucosal side was measured. Maximal values were attained when the Na concentration was 10 mM for SCC and 30 mM for p.d.2. Amphotericin B increased SCC across bladders bathed on their mucosal surface with isotonic (115 mM) NaCl solution and this effect was not inhibited by cyanide and iodoacetate. The osmotic permeability of the bladder was also increased by amphotericin B.3. Vasopressin and aldosterone increased sodium transport from solutions of low Na concentration, but amphotericin B was ineffective until a level of about 40-60 mM was present.4. The evidence suggests two pathways for sodium transport across the bladder distinguished by differences in their electrochemical gradients with the fluid at the mucosal side.