RESUMEN
In the freshly isolated rat nephron, the effect of endothelin-1, -2 and -3 (ET-1, -2 and -3) on cytosolic free calcium concentration ((Ca2+)i) was determined using the fluorescent indicator Fura-2/AM. (Ca2+)i increase was investigated in 9 parts of the single nephron including glomerulus (Glm), S1, S2, S3, Cortical and medullary thick ascending limb and cortical (CCT) and outer medullary collecting tubule (OMCT). Endothelins increased (Ca2+)i in Glm (ET-1; 127+/-17%, ET-2; 93+/-5%, ET-3; 169+/-17%), CCT (ET-1; 30+/-6%, ET-2; 38+/- 19%, ET-3; 158+/-18%) and OMCT (ET-1; 197+/- 11%, ET-2; 195+/- 11%, ET-3; 215+ 37%) at 10(-7) M. In OMCT, ET-1 and ET-2 increased (Ca2+)i in a dose-dependent manner (10(-10) ~ 10(-6) M). To the contrary, ET-3-induced (Ca2+)i rise was begun from 10(-12) M. BQ-123Na, an antagonist of ETA receptor, at 10(-4) M inhibited about 30% of (Ca2+)i rise induced by ET-1 and -3. Binding experiments using (125I)ET-3 showed the existence of ETB receptor in OMCT. This binding was replaced by ET-1, ET-2 or ET-3 by the almost same degree but not by angiotensin II or vasopressin.