ENDOTHELIN RECEPTOR SUBTYPES AND STIMULATION OF ALDOSTERONE SECRETION

Endothelins (ETs) are 21-amino add peptides with two disulfide bonds that have powerful vasoactive properties. We have previously shown the presence of a specific, high-affinity, saturable receptor for porcine or human endothelin (ET-1) in cultured calf zona glomerulosa cells. ET-1 was a stimulator of aldosterone secretion although not as powerful as angiotensin 11. Incubations of cultured calf zona glomerulosa cells with Sarafotoxin S6b (S6b), a snake venom that has a structure highly homologous to ET-1, stimulated aldosterone secretion with a potency similar to that of ET-1. Binding of [125I] ET-1 to the adrenal receptor gave a kd of 0.17±0.05 nM and Bmax of 36±8.5 (mol/well (n=4). Displacement of [125I]ET-1 by unlabeled ETs and S6b showed that the concentrations needed to displace 50% of the tracer were 0.3 nM for ET-1, 0 J nM for ET-2, 10 nM for S6b, and 100 nM for ET-3. Binding of [125I]S6b to cultured adrenal cells revealed a receptor with a Kd of 0.05±0.01 nM and a Bmax of 8±2 fmol/well (n=4). Displacement of [12iI]S6b by unlabeled ETs and S6b showed that the concentrations needed to displace 50% of the tracer were 0.03 nM for S6b, 0.06 nM for ET-1, 0.04 nM for ET-2, and 0.05 nM for ET-3. Unlabeled ET-1 and ET-2 preferentially down-regulated the binding of [125I]ET-1, and S6b preferentially down-regulated the binding of [125I]S6b. Labeled S6b (which is unlikely to exist in mammals) served as a tool to uncover the high-affinity receptor for ET-1 (ET-lor receptor), which is likely responsible for stimulation of aldosterone secretion. The second receptor or lower affinity, higher capacity receptor (ET-l/f receptor) has an unclear function at this time. © 1990 American Heart Association, Inc.