Glibenclamide-sensitive mechanism is involved in helodermin-produced vasodilatation in rat mesenteric artery

Helodermin-caused vascular relaxation was simultaneously measured with intracellular Ca2+ concentration (Ca2+]i) in rat mesenteric artery. Helodermin caused concentration-dependent relaxation in the mesenteric artery preconstricted with norepinephrine (NE). Helodermin-caused relaxation was accompanied by decrease in Ca2+]i, D-cis-Diltiazem, a Ca2+ channel blocker, also lowered the Ca2+]i and tension increased by NE. However, helodermin relaxed the artery more efficiently than D-cis-diltiazem, suggesting that the peptide decreased myofilament Ca2+ sensitivity. The vascular relaxation and the corresponding decrease in Ca2+]i induced by helodermin were partly, but significantly attenuated by glibenclamide. Helodermin-induced vascular responses were mimicked by vasoactive intestinal polypeptide (VIP) or forskolin. Furthermore, helodermin increased cAMP contents in the mesenteric artery. These findings show that vasodilatation induced by helodermin is attributable to lowered Ca2+]i of arterial smooth muscle partly through the activation of glibenclamide-sensitive K+ channels, and to decrease in the myofilament Ca2+ sensitivity. The increase in the cellular cAMP content probably plays a key role in the peptide-induced vasorelaxation.