Cyclosporin A depolarizes cytoplasmic membrane potential and interacts with Ca2+ ionophores

Cytoplasmic membrane potential of mouse lymphocytes was determined with flow cytometry and fluorescence spectroscopy using 3,3'-dihexylcarbocyanine iodide (DiOC6(3)). The amount of this lipophilic cation incorporated into the cytoplasmic membrane is dependent upon the transmembrane potential, so the dye is suitable for continuous monitoring of this parameter, under controlled conditions. Membrane potential of the cells was decreased in the presence of cyclosporin A and cyclosporin G in a dose-dependent manner. However, the depolarization caused by Ca2+ ionophores, ionomycin and A23187, was reduced in the presence of cyclosporin A. Electron spin resonance spectroscopy with 5-doxylstearic acid as a probe indicated that cyclosporin A decreased the apparent motional freedom of membrane lipids. These data suggest incorporation of cyclosporin A into the cytoplasmic membrane, causing changes in ion fluxes. The membrane potential change induced by cyclosporin A may have selective biological consequences in certain subpopulations of lymphocytes.