Dual effects of amphotericin B on ion permeation in toad urinary bladder epithelium

The mechanisms of action of amphotericin B on the electrical properties of the toad urinary bladder epithelium were studied with microelectrode techniques. Cell membrane and transepithelial electrical potentials and resistances were measured in the absence and in the presence of the drug during exposure to bathing mediums of different ionic compositions. As observed previously by other investigators, amphotericin B produces a dramatic decrease of transepithelial electrical resistance (Rt) and an increase of the rate of sodium transport. Our results indicate that the effect of the drug on Rt depends in part on an increase in Na conductance across the luminal cell membrane (amiloride-insensitive), but is caused mainly by an increase of ionic conductances (with the sequence GK greater than GNa greater than G choline greater than GCI) at a site in parallel with the impaled cells (i.e., across a cell type not investigated by the microelectrode measurements or across the paracellular pathway.