Contribution of Na+ -Ca2+ exchanger to pinacidil-induced relaxation in the rat mesenteric artery.
1 Pinacidil relaxes blood vessels through opening the K(ATP) channels with a resultant membrane hyperpolarization and inhibition of Ca(2+) influx. The aim of this study was to examine the mechanisms thereby pinacidil induces K(+) channel-independent relaxation in isolated endothelium-denuded rat mesenteric artery. 2 Pinacidil-induced relaxation was inhibited by glibenclamide (1-10 micro M) in phenylephrine-preconstricted rings, but was unaffected by glibenclamide after inhibition of K(+) channels and VGCCs. Pinacidil-induced K(+) channel-independent relaxation remained unchanged after treatment with cyclopiazonic acid (10 micro M), thapsigargin (1 micro M), ouabain (100 micro M), propranolol (10 micro M), Rp-cAMPS triethylamine (30 micro M), L-NNA (100 micro M), or ODQ (10 micro M). 3 Pinacidil induced more relaxant effect in the presence of nifedipine than in the presence of 60 mM K(+) plus nifedipine. Pretreatment with Na(+)-Ca(2+) exchanger inhibitors, nickel (30-300 micro M) or benzamil (20 micro M) attenuated pinacidil-induced relaxation in normal or in nifedipine-containing solution. Pinacidil (1 micro M) produced less relaxant effect with decreasing extracellular Na(+) concentration. Na(+)-free condition abolished the inhibitory effect of benzamil. Both nickel and benzamil inhibited pinacidil-induced relaxation in the presence of glibenclamide (10 micro M). Nickel (300 micro M) did not affect the relaxant response to sodium nitroprusside. 4 Pinacidil relaxed the rings preconstricted by active phorbol and U46619 with similar potency. 5 The present results indicate that stimulation of the forward mode Na(+)-Ca(2+) exchange pathway is in part responsible for pinacidil-induced K(+) channel-independent vasorelaxation. Pinacidil also induces K(+) channel-dependent but VGCCs-independent relaxation. The PKC-mediated cellular pathway may be a target site for pinacidil only in higher concentrations.
Tsang
Suk Ying
SY
Department of Physiology, Chinese University of Hong Kong, Hong Kong, China.
Yao
Xiaoqiang
X
Wong
Chi Ming
CM
Au
Chak Leung
CL
Chen
Zhen Yu
ZY
Huang
Yu
Y
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D017538:Mesenteric Artery, Superior / Q000187:drug effects* / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D020110:Pinacidil / Q000008:administration & dosage / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors* / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D019831:Sodium-Calcium Exchanger; D014665:Vasodilator Agents; D020110:Pinacidil; D011493:Protein Kinase C