ABSTRACT
Aim To investigate the effects of midazolam on porcine isolated coronary artery rings pre-contracted by potassium chloride(KCl)and the possible mechanism.Methods The vessel tension recorder system was used.Isotonic tension of porcine isolated coronary artery rings precontracted by KCl(30 mmol·L-1)was recorded.The vasorelaxing action of midazolam and effects of various drugs were observed in the rings.Results Midazolam(3×10-6～1×10-4 mol·L-1)respectively concentration-dependently reduced the contraction induced by KCl,and there was significant difference between the rings with intact and denude endothelium(P<0.05).On KCl-induced precontraction,midazolam′s relaxation was depressed by L-NAME and the blend of L-NAME and L-Arg(P<0.05),but was not affected by Indo,L-Arg and 1400W.The contraction was not prevented by pretreatment with the inhibitor of Na+/Ca2+ exchanger(KB-R7943).The inhibitor of KATP(Gli)restrained the diastolic function of midazolam(P<0.05),while the inhibitor of BKCa(TEA),Kir(BaCl2),KV(4-AP)had no obvious effect.Conclusions Midazolam produces remarkable vasodilatation on KCl pre-contracted porcine isolated coronary artery rings.Its relaxtion effect is via concentration-dependent and endothelium-dependent mechanisms and relevant to the production of NO.Na+/Ca2+ exchanger is not involved midazolam′s vasodilatation on KCl pre-contracted porcine coronary artery rings.The relaxant mechanism of midazolam may be concerned with KATP.The Kir,BKCa and KV may be not involved.