Cyclosporine increases endothelin-1 binding site density in cardiac cell membranes.

When used in high concentrations, the immunosuppressive agent cyclosporine A has toxic side effects, including cardiac fibrosis and calcification. Cyclosporine-treated mice were used to investigate whether a cyclosporine dose regime which produces cardiac fibrosis and calcification alters the density of the specific binding sites for the endothelial-derived vasoconstrictor polypeptide, endothelin-1. After twenty-one days of treatment the endothelin-1 binding site density in cardiac cell membranes was increased, without any change in selectivity. This increase in endothelin-1 binding site density could contribute to the cytotoxic effects of cyclosporine.