DIFFERENTIAL-EFFECTS OF BQ-123 AGAINST ENDOTHELIN-1 AND ENDOTHELIN-3 ON THE RAT VAS-DEFERENS - EVIDENCE FOR AN ATYPICAL ENDOTHELIN RECEPTOR

1 Endothelin-1 and endothelin-3 enhanced concentration-dependently the rat vas deferens twitch response to electrical stimulation, endotheli n-1 being three times more potent. Sarafotoxin S6c was at least 200 ti mes less active than endothelin-1. 2 The response to endothelin was an tagonized in a competitive manner by the supposedly selective ET(A) re ceptor antagonist, BQ-123 (pA2:7.0 +/- 0.1). In contrast, the endothel in-1 concentration-response curve was only shifted two fold in the pre sence of 10 mum BQ-123, while no effect was observed at 1 muM. 3 This evidence suggests the rat vas deferens contains an endothelin receptor not conforming to the ET(A)/ET(B) receptor subtype classification so far proposed.