title: Chronic U50,488H abolishes inositol 1,4,5-trisphosphate and intracellular Ca2+ elevations evoked by kappa-opioid receptor in rat myocytes.
abstract: The inositol 1,4,5-trisphosphate (IP3) content and intracellular free Ca2+ ([Ca2+]i) level in response to kappa-opioid receptor stimulation with selective kappa-opioid receptor agonists, dynorphin-(1-13) and trans-3,4-dichloro-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeacetamidel (U50,488H) were determined in ventricular myocytes. Both IP3 and [Ca2+]i were increased following kappa-opioid receptor stimulation. The responses of IP3 and [Ca2+]i to kappa-opioid receptor stimulation were abolished in myocytes of rats that had received chronic injection of U50,488H for 4 days. kappa-Opioid receptor stimulation with U50,488H also reduced the [Ca2+]i transient, induced by electrical stimulation and caffeine, both known to mobilize [Ca2+]i. The effect was abolished after the myocytes had been incubated with U50,488H at a subthreshold concentration for its effect on [Ca2+]i for 24 h. The present study showed for the first time that, upon the development of tolerance to a kappa-opioid receptor agonist, the responses of IP3 and [Ca2+]i to kappa-opioid receptor stimulation were abolished. The lack of response in [Ca2+]i was due to a failure of mobilization of Ca2+ from its intracellular pool. Further study is needed to determine the events that occur after the kappa-opioid receptor stimulation to production of IP3 upon the development of tolerance to a kappa-opioid.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Hong Kong, Hong Kong.
authors.forename: J Z
authors.initials: JZ
authors.lastname: Sheng
authors.forename: T M
authors.initials: TM
authors.lastname: Wong
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004399:Dynorphins / Q000494:pharmacology; D004558:Electric Stimulation; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017473:Receptors, Opioid, kappa / Q000819:agonists / Q000187:drug effects* / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D002110:Caffeine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C026843:dynorphin (1-13); D004399:Dynorphins; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium