title: Effect of the polyene antibiotic filipin and the calcium ionophore A23187 on sodium transport in isolated frog skin (Rana temporaria).
abstract: Addition of filipin (50 micrometer) 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 micrometer) 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 micrometer) 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 ionophores 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.
mesh_terms: D000200:Action Potentials; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001001:Anura; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D005260:Female; D005372:Filipin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D008433:Mathematics; D008564:Membrane Potentials; D011090:Polyenes / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D011896:Rana temporaria; D012867:Skin / Q000378:metabolism*; D012879:Skin Physiological Phenomena; D012964:Sodium / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D011090:Polyenes; D014667:Vasopressins; D000001:Calcimycin; D005372:Filipin; D012964:Sodium; D014357:Trypsin; D011188:Potassium; D002118:Calcium