Differential effects of BQ‐123 against endothelin‐1 and endothelin‐3 on the rat vas deferens: evidence for an atypical endothelin receptor

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Abstract
1 Endothelin-1 and endothelin-3 enhanced concentration-dependently the rat vas deferens twitch response to electrical stimulation, endothelin-1 being three times more potent. Sarafotoxin S6c was at least 200 times less active than endothelin-1. 2 The response to endothelin was antagonized in a competitive manner by the supposedly selective ETA receptor antagonist, BQ-123 (pA2:7.0 ± 0.1). In contrast, the endothelin-1 concentration-response curve was only shifted two fold in the presence of 10 μm BQ-123, while no effect was observed at 1 μm. 3 This evidence suggests the rat vas deferens contains an endothelin receptor not conforming to the ETA/ETB receptor subtype classification so far proposed.