EFFECT OF THE POLYENE ANTIBIOTIC FILIPIN AND THE CALCIUM IONOPHORE A23187 ON SODIUM-TRANSPORT IN ISOLATED FROG SKIN (RANA-TEMPORARIA)

Addition of filipin (50 μm) to the inside bathing solution of the frog skin resulted in a transient increase in the active sodium transport [measured as short-circuit current (SCC)]. The filipin-induced increase in the SCC required the presence of calcium. The calcium ionophore A23187 (4 μm) also induced a transient increase in the SCC. After the activation of the SCC by A23187, the SCC could not be activated by filipin. This indicates that the polyene antibiotic filipin acts as a calcium ionophore. Higher concentrations (40 μm) of A23187 resulted in a shrinking of the cells in the transporting cell layer. A23187 also increased the potassium-42 exchange in the isolated epithelium. It is suggested that calcium inophores enhanced the intracellular calcium concentration; this increase in the calcium concentration resulted in an increase in the potassium permeability of the inward-facing membrane. The increase in the potassium permeability might explain the observed increase in the SCC. © 1978 Springer-Verlag New York Inc.