Localization of [125I]endothelin-1 in rat tissues observed by electron-microscopic radioautography

[125I]Endothelin-1 (ET-1) was administered intravenously into rats, and binding sites in various tissues were examined by electron-microscopic radioautography. Labeling was observed predominantly on the glomerular fenestrated endothelial cells of kidney, alveolar capillary endothelial cells of lung, fat-storing cells in the sinusoids of liver, and subepithelial myofibroblasts of the small intestine. At first, silver grains were observed mostly on the plasmalemma of these cells and with time translocated into the cytoplasm of these cells. Myofibroblasts of the small intestine were cultured to study the cellular effects of ET. By fura-2 fluorescence method, transient increase and oscillation of intracellular Ca2+ level were observed in the cultured myofibroblasts following the application of ET-1 or endothelin-3 (ET-3). These results suggest that ET induces diverse physiological reactions in specific cells of various tissues.