Characterization of the Endothelin Receptors of Rat Myometrial Plasma Membranes

Binding of 125I-endothelin-1 (human endothelin) to purified rat myometrial plasma membranes was assayed. Analysis of binding data displayed binding to two groups of receptors, a high affinity low capacity pool (Kd = 0.22 nM), and a low affinity high capacity pool (Kd = 173 nM). The high affinity pool most likely originated from contamination with vascular cell membranes, and it was concluded that the endothelin affinity to myometrial tissue is low, which is in agreement with earlier reports on the uterotonic potency.