ATP-sensitive potassium channels do not mediate vasorelaxation by acetylcholine or iloprost

The influence of glibenclamide(GBC), a blocker of ATP-sensitive K+ channells, on relaxation caused by cromakalin(CKL), acetylcholine (ACh) and iloprost (ILO) was assessed in aortic rings (AR) with (E+) or without endotheliium (E-) and in the perfused arterial mesentery (MES) of the rat. In AR preconstricted with noradrenaline, CKL(0.03-10 *M) and ILO (5.5 nM) caused graded vasodilations which were not modified by endothelium removal. ACh(0.01-3 *M) only relaxed E+AR preparations. GBC (3*M) markedly reduced responses to CKL in E+AR and E-AR, but did not affect vasodilation induceds by ILO in E-AR and by ACH in E+AR. In MES preconstricted with methoxamine, bolus injections of CKL (10 or 30 nmol) or ACh (0.03-1nmol) caused graded reductions of perfusion pressure. Only the responses to CKL were significantly inhibited by GBC (10 *M). We conclude that AR and MES contain functional ATP-sensitive K+ channels, which, however, do not play a significant role in the endothelium-dependent vasodilation triggered by ACh or in the endothelium-indipendent relaxation induced by ILO