Characterization of cloned human endothelin receptors

Two subtypes of human endothelin receptors, ETA and ETB, have been cloned and stably expressed in Chinese Hamster Ovary cells. These receptors have been characterized by [125I]-endothelin-1 binding and phosphatidyl inositol hydrolysis using the potent peptidyl ETA antagonists BQ-123 and BQ-153, as well as the potent ETB agonist, sarafotoxin S6c. In binding studies, Ki values for BQ-123 and BQ-153 are 17 nM and 13 nM for ETA compared to 11,100 nM and 7200 nM for ETB. Conversely, Ki values for sarafotoxin S6c are 2800 nM for ETA and 0.29 nM for ETB. Endothelin-1 stimulates phosphatidyl inositol hydrolysis in cells expressing either ETA or ETB with EC50 values of 0.2-0.3 nM, while sarafotoxin S6c stimulates phosphatidyl inositol hydrolysis only in ETB expressing cells with an EC50 value of 0.2 nM, consistent with the binding data. Comparison of binding data for the cloned and expressed human receptors with binding data for receptors obtained from human tissues indicates the cloned and expressed receptors are essentially indistinguishable from the naturally occurring receptors.