Abstract

Specific binding sites for synthetic endothelin (ET) isoforms, ET-1 and ET-3 were studied in a bovine adrenomedullary chromaffin cell-rich preparation, and compared to those on A10 cells, a vascular smooth muscle cell line. Both [125I]ET-1 and [125I]ET-3 (2.5 x 10(-11) M) specifically bound to a single class of binding sites on the chromaffin cell preparation (apparent Kd 2.3 x 10(-10) and 1.4 x 10(-10) M, respectively), and the binding of both peptides was inhibited competitively by unlabeled ET-1, ET-3 and sarafotoxin S6b to an equal degree (IC50 values in the range 1.2 x 10(-10) to 3.1 x 10(-10) M). In contrast, only [125I]ET-1 (2.5 x 10(-11) M) specifically bound to A10 cells, to a single class of binding sites with apparent Kd of 1.5 x 10(-10) M. The same concentration of [125I]ET-3 displayed no evidence of specific binding. The binding of [125]ET-1 to A10 cells was inhibited competitively by unlabeled ET isoforms with the following order of potency: ET-1 (IC50, 3.1 x 10(-10) M) greater than Sarafotoxin S6b (IC50, 3.1 x 10(-9) M) greater than ET-3 (188 x 10(-9) M). ET-1 and ET-3 dose-dependently induced an increase in total inositol phosphate accumulation (the EC50 value of ET-1 was 1.3 x 10(-9) M). Neither ET-1 nor ET-3, up to 100 nM, affected the total inositol phosphate content of chromaffin cells.(ABSTRACT TRUNCATED AT 250 WORDS)