title: Opioid receptor antagonists modulate Ca2+-activated K+ channels in mesenteric arterial smooth muscle cells of rats in hemorrhagic shock.
abstract: Previous study has indicated a significant enhancement of activity of large-conductance Ca2+-activated K+ channel (BKCa) in mesenteric arterial vascular smooth muscle cells isolated from rats in vascular hyporesponsive stage of hemorrhagic shock. In the present study, the effect of opioid receptor antagonism on BKCa activity in the vascular smooth muscle cells of rats in the hyporesponse stage of hemorrhagic shock was investigated by using inside-out configuration of the patch-clamp technique. The results showed that naloxone (10 microM) down-regulated the activity of BKCa by reducing open probability (Po) and open frequency of the channels. The reduction of Po resulted from a decrease of mean open time and an increase of the slow closed time constant. Naltrindole and nor-binaltorphimine (100 nM) had the similar effects to that of naloxone, but no significant effect of beta-funaltrexamine (100 nM) on the activity of the channels could be found. These results suggest that delta- and kappa-opioid receptors, but not mu-receptors, may be involved in the regulation of BKCa in vascular hyporesponse stage, and that inhibition of BKCa may be one of the mechanisms of the opioid receptor antagonists improving the response of resistance arteries to vasoactive stimulants during the decompensatory stage of hemorrhagic shock.
authors.affiliation: Institute of Surgery, Daping Hospital, Department of Pharmacology, Third Military Medical University, Chongqing, 400042, People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Kai
authors.forename: Zhong-Feng
authors.initials: ZF
authors.lastname: Wang
authors.forename: De-Yao
authors.initials: DY
authors.lastname: Hu
authors.forename: Yu-Liang
authors.initials: YL
authors.lastname: Shi
authors.forename: Liang-Ming
authors.initials: LM
authors.lastname: Liu
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004594:Electrophysiology; D007700:Kinetics; D008564:Membrane Potentials; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012771:Shock, Hemorrhagic / Q000188:drug therapy / Q000378:metabolism*
chemical_list: D009292:Narcotic Antagonists; D015221:Potassium Channels; D009270:Naloxone; C051844:norbinaltorphimine; D009271:Naltrexone; C024524:beta-funaltrexamine; C055382:naltrindole; D002118:Calcium