title: Calcium stimulates opioid receptor agonism in rat cardiac sarcolemma.
abstract: We have found that calcium stimulates, in a dose-dependent manner, the binding of opioid to kappa and delta receptors in sarcolemma from rat's ventricles isolated by hypotonic lithium bromide shock. Opioid binding was measured using [3H]-diprenorphine as a radioligand. The delta-selective agonist [D-Ala2, D-Leu5]-enkephalin and the kappa-selective agonist U-50, 488H both inhibited control and Ca(2+)-stimulated [3H]-diprenorphine binding to the sarcolemma, whereas [D-Ala2,MePhe4,Gly-(ol)5]-enkephalin was ineffective. The stimulatory effect of calcium increased the maximal binding capacity without affecting the affinity of the receptor for the ligand.
authors.affiliation: Department of Biochemistry, University of Bologna, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Ventura
authors.forename: C
authors.initials: C
authors.lastname: Guarnieri
authors.forename: L
authors.initials: L
authors.lastname: Bastagli
authors.forename: P
authors.initials: P
authors.lastname: Bernardi
authors.forename: P
authors.initials: P
authors.lastname: Puddu
authors.forename: C M
authors.initials: CM
authors.lastname: Caldarera
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004174:Diprenorphine; D004305:Dose-Response Relationship, Drug; D009206:Myocardium / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D012508:Sarcolemma / Q000378:metabolism*; D013268:Stimulation, Chemical; D014316:Tritium
chemical_list: D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D014316:Tritium; D004174:Diprenorphine; D002118:Calcium