The presence of functional endothelin ETB receptors was investigated in rat isolated mesenteric resistance arteries. Neither endothelin-3 (0.1-100 nM) nor the endothelin ETB selective agonists sarafotoxin S6c and BQ 3020 (both 1-100 nM) induced any measurable hyperpolarization or relaxation in stimulated (alpha 1-adrenoceptor agonist; phenylephrine) or unstimulated arteries. In both cases, the subsequent addition of acetylcholine (1 microM) hyperpolarized the membrane potential by 10-20 mV and totally reversed any contraction which was present. These results indicate that the endothelin ETB-mediated vasodilatation observed in the intact mesenteric bed does not reflect hyperpolarization of smooth muscle cells in resistance arteries arising from the mesenteric artery.
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