LACK OF ENDOTHELIN ET(B) RECEPTOR-MEDIATED SMOOTH-MUSCLE HYPERPOLARIZATION IN RAT MESENTERIC RESISTANCE ARTERIES

The presence of functional endothelin ET(B) receptors was investigated in rat isolated mesenteric resistance arteries. Neither endothelin-3 (0.1-100 nM) nor the endothelin ET(B) selective agonists sarafotoxin S 6c and BQ 3020 (both 1-100 nM) induced any measurable hyperpolarizatio n or relaxation in stimulated (alpha(1)-adrenoceptor agonist; phenylep hrine) or unstimulated arteries. In both cases, the subsequent additio n of acetylcholine (1 mu M) hyperpolarized the membrane potential by 1 0-20 mV and totally reversed any contraction which was present. These results indicate that the endothelin ET(B)-mediated vasodilatation obs erved in the intact mesenteric bed does not reflect hyperpolarization of smooth muscle cells in resistance arteries arising from the mesente ric artery.