Endothelin Increases Intracellular Free Calcium in Isolated Rat Nephron

Endothelin Increases Intracellular Free Calcium in Isolated Rat Nephron

<P> In the freshly isolated rat nephron, the effect of endothelin-1, -2 and -3 (ET-1, -2 and -3) on cytosolic free calcium concentration ([Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB>) was determined using the fluorescent indicator Fura-2/AM. [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase was investigated in 9 parts of the single nephron including glomerulus (Glm), S<SUB>1</SUB>, S<SUB>2</SUB>, S<SUB>3</SUB>, cortical and medullary thick ascending limb and cortical (CCT) and outer medullary collecting tubule (OMCT). Endothelins increased [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> 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<SUP>-7</SUP> M. In OMCT, ET-1 and ET-2 increased [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> in a dose-dependent manner (10<SUP>-10</SUP>∼10<SUP>-6</SUP> M). To the contrary, ET-3-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> rise was begun from 10<SUP>-12</SUP> M. BQ-123Na, an antagonist of ET<SUB>A</SUB> receptor, at 10<SUP>-4</SUP> M inhibited about 30% of [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> rise induced by ET-1 and -3. Binding experiments using [<SUP>125</SUP>I]ET-3 showed the existence of ET<SUB>B</SUB> 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.