Potassium channels contribute to the increased sensitivity of the rabbit carotid artery to hydrogen sulfide in diabetes

Hydrogen sulfide (H2S) is a potential endothelium-derived hyperpolarizing factor (EDHF) and adventitium- or adipocyte-derived relaxing factor (ADRF) which vasorelaxant action is mediated by potassium channels. H2S could also play an important role in the pathophysiology of diabetic cardiovascular complications. The present study has investigated the influence of alloxan-induced diabetes on the role of potassium channels mediating the relaxant response of the rabbit carotid artery to NaHS, a donor of H2S. NaHS (10(-8) -3 x 10(-5) M) relaxed phenylephrine-precontracted carotid arteries, with higher potency in diabetic than in control rabbits. The selective blockers of potassium channels charybdotoxin, 4-amynopiridine and glibenclamide significantly inhibited the relaxant action of NaHS in diabetic rabbits, but not in control rabbits. When compared to control rabbits, carotid arteries from diabetic rabbits showed significantly reduced expression of big conductance Ca+2- activated potassium channels (BKca) significantly enhanced expression of intermediate conductance Ca+2- activated potassium channels (IKca) and not significant different expression of voltage-sensitive potassium channels (K-v) and ATP-sensitive potassium channels (K-ATP). These results suggest that an enhanced role of IKca, K-v and K-ATP potassium channels could be involved in the increased sensitivity of the rabbit carotid artery to H2S in diabetes.