{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,6,4]],"date-time":"2025-06-04T20:28:10Z","timestamp":1749068890886},"reference-count":0,"publisher":"Canadian Science Publishing","issue":"5","license":[{"start":{"date-parts":[[1989,5,1]],"date-time":"1989-05-01T00:00:00Z","timestamp":609984000000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/www.nrcresearchpress.com\/page\/about\/CorporateTextAndDataMining"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Can. J. Physiol. Pharmacol."],"published-print":{"date-parts":[[1989,5,1]]},"abstract":"<jats:p> The effect of several opioid drugs was tested on the K<jats:sup>+<\/jats:sup> contractures in frog's skeletal muscle. These contractures are produced by the entrance of extracellular Ca<jats:sup>2+<\/jats:sup> ions via the voltage-dependent, slow Ca<jats:sup>2+<\/jats:sup> channels located in the T tubules. Morphine and other opioid agonists in concentrations ranging from 10<jats:sup>\u221210<\/jats:sup> to 10<jats:sup>\u22125<\/jats:sup>\u2002M inhibited K<jats:sup>+<\/jats:sup> contractures. The stereoisomers, dextrorphan and levorphanol, were found to have identical potency in inhibiting high K<jats:sup>+<\/jats:sup> contractures, suggesting that this was a nonstereospecific blockade of voltage-dependent calcium channels by the opioid drugs despite the low effective drug concentrations. In agreement with this conclusion it was found that the inhibition of K<jats:sup>+<\/jats:sup> contractures by the opioids was not antagonized by naloxone. It also was observed using a sucrose gap apparatus that these opioid drugs in concentrations used to block the high K<jats:sup>+<\/jats:sup> contractures did not reduce the K<jats:sup>+<\/jats:sup>-induced membrane depolarization. Raising the bathing solution Ca<jats:sup>2+<\/jats:sup> concentration from 1.08 to 5\u2002mM produced a reversal of the opioid-induced block of K<jats:sup>+<\/jats:sup> contractures. Finally it was shown that while opioids completely blocked K<jats:sup>+<\/jats:sup> contractures, they did not produce any effect on caffeine contractures showing that opioids do not deplete intracellular Ca<jats:sup>2+<\/jats:sup> stores or inhibit the release of Ca<jats:sup>2+<\/jats:sup> from intracellular sarcoplasmic reticulum stores. It was concluded that several opioid drugs in very low concentrations block K<jats:sup>+<\/jats:sup> contractures in frog's skeletal muscle by a nonstereospecific block of voltage-dependent slow calcium channels.Key words: opioids, calcium channels, contractures, skeletal muscle, opiate receptors, narcotics. <\/jats:p>","DOI":"10.1139\/y89-070","type":"journal-article","created":{"date-parts":[[2011,4,24]],"date-time":"2011-04-24T08:56:31Z","timestamp":1303635391000},"page":"435-441","source":"Crossref","is-referenced-by-count":1,"title":["Blockade of K<sup>+<\/sup> contractures in skeletal muscle by opioid drugs: a nonstereospecific effect"],"prefix":"10.1139","volume":"67","author":[{"given":"Tushar G.","family":"Kokate","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"George B.","family":"Frank","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"155","container-title":["Canadian Journal of Physiology and Pharmacology"],"original-title":[],"language":"en","link":[{"URL":"http:\/\/www.nrcresearchpress.com\/doi\/pdf\/10.1139\/y89-070","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2020,1,5]],"date-time":"2020-01-05T15:14:13Z","timestamp":1578237253000},"score":1,"resource":{"primary":{"URL":"http:\/\/www.nrcresearchpress.com\/doi\/10.1139\/y89-070"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1989,5,1]]},"references-count":0,"journal-issue":{"issue":"5","published-print":{"date-parts":[[1989,5,1]]}},"alternative-id":["10.1139\/y89-070"],"URL":"https:\/\/doi.org\/10.1139\/y89-070","relation":{},"ISSN":["0008-4212","1205-7541"],"issn-type":[{"value":"0008-4212","type":"print"},{"value":"1205-7541","type":"electronic"}],"subject":[],"published":{"date-parts":[[1989,5,1]]}}}