Luminal and basolateral endothelin inhibit chloride reabsorption in the mouse thick ascending limb via a Ca2+-Independent Pathway

1 The recent localization of endothelin synthesis and receptors in the thick ascending limb (TAL) prompted us to investigate a possible autocrine and/or paracrine effect of this agent. The net chloride flux (JCl) has been determined in isolated cortical and medullary TALs by the in vitro microperfusion technique. 2 In both segments, endothelin 1 (ET-1) at 10−8m in the bath significantly decreased JCl, an effect which was partially reversible and observed at concentrations equal to or greater than 10−13m. 3 This (JCl inhibition (by 33.9 ± 3.2%) was blocked by BQ788 and was also observed with sarafotoxin 6C and ET-3, indicating that endothelin receptor B (ETB) are present in TAL. 4 ET-1 did not affect cAMP content under basal or hormone-stimulated conditions. The presence of a prostaglandin synthesis inhibitor also did not prevent the ET-1 action on JCl. 5 The ET-1-induced inhibition of JCl was prevented by protein kinase C inhibitors (staurosporine or GF 109203) and was reproduced by diacylglycerol analogues (OAG and DiC8). However, ET-1 failed to increase intracellular Ca2+ concentration. 6 Addition of ET-1 or ET-3 to the apical surface induced a decrease of JCl through ETB receptors, an effect which was not additive with that induced by basolateral ET-1, and was not concomitant with an increase in intracellular Ca2+ concentration. 7 It is concluded that the basolateral and luminal inhibitions of JCl by ET-1 in TAL, through ETB receptors, is mediated by a protein kinase C activation which is independent of intracellular Ca2+ increase.