title: Inhibition of Ca2+ channel current by mu- and kappa-opioid receptors coexpressed in Xenopus oocytes: desensitization dependence on Ca2+ channel alpha 1 subunits.
abstract: 1. Desensitization of mu- and kappa-opioid receptor-mediated inhibition of voltage-dependent Ca2+ channels was studied in a Xenopus oocyte translation system. 2. In the oocytes coexpressing kappa-opioid receptors with N- or Q-type Ca2+ channel alpha 1 and beta subunits, the kappa-agonist, U50488H, inhibited both neuronal Ca2+ channel current responses in a pertussis toxin-sensitive manner and the inhibition was reduced by prolonged agonist exposure. 3. More than 10 min was required to halve the inhibition of Q-type channels by the kappa-agonist. However, the half-life for the inhibition of N-type channels was only 6 +/- 1 min. In addition, in the oocytes coexpressing mu-opioid receptors with N-type or Q-type channels, the uncoupling rate of the mu-receptor-mediated inhibition of N-channels was also faster than that of Q-type channels. 4. In the oocytes coexpressing both mu- and kappa-receptors with N-type channels, stimulation of either receptor resulted in a cross-desensitization of the subsequent response to the other agonist. Treatment of oocytes with either H-8 (100 microM), staurosporine (400 nM), okadaic acid (200 nM), phorbol myristate acetate (5 nM) or forskolin (50 microM) plus phosphodiesterase inhibitor did not affect either the desensitization or the agonist-evoked inhibition of Ca2+ channels. 5. These results suggest that the rate of rapid desensitization is dependent on the alpha 1 subtype of the neuronal Ca2+ channel, and that a common phosphorylation-independent mechanism underlies the heterologous desensitization between opioid receptor subtypes.
authors.affiliation: Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyoto University, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kaneko
authors.forename: N
authors.initials: N
authors.lastname: Yada
authors.forename: K
authors.initials: K
authors.lastname: Fukuda
authors.forename: M
authors.initials: M
authors.lastname: Kikuwaka
authors.forename: A
authors.initials: A
authors.lastname: Akaike
authors.forename: M
authors.initials: M
authors.lastname: Satoh
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000187:drug effects*; D011494:Protein Kinases / Q000378:metabolism; D011759:Pyrrolidines / Q000494:pharmacology; D017473:Receptors, Opioid, kappa / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D013997:Time Factors; D014981:Xenopus
chemical_list: D000959:Antihypertensive Agents; D015220:Calcium Channels; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D011494:Protein Kinases