delta-Opioid receptors are more efficiently coupled to adenylyl cyclase than to L-type Ca(2+) channels in transfected rat pituitary cells.
Opioid receptors often couple to multiple effectors within the same cell. To examine potential mechanisms that contribute to the specificity by which delta-receptors couple to distinct intracellular effectors, we stably transfected rat pituitary GH(3) cells with cDNAs encoding for delta-opioid receptors. In cells transfected with a relatively low delta-receptor density of 0.55 pmol/mg of protein (GH(3)DOR), activation of delta-receptors produced inhibition of adenylyl cyclase activity but was unable to alter L-type Ca(2+) current. In contrast, activation of delta-receptors in a clone that contained a higher density of delta-receptors (2.45 pmol/mg of protein) and was also coexpressed with mu-opioid receptors (GH(3)MORDOR), resulted in not only the expected inhibition of adenylyl cyclase activity but also produced inhibition of L-type Ca(2+) current. The purpose of the present study was to determine whether these observations resulted from differences in delta-opioid receptor density between clones or interaction between delta- and mu-opioid receptors to allow the activation of different G proteins and signaling to Ca(2+) channels. Using the delta-opioid receptor alkylating agent SUPERFIT, reduction of available delta-opioid receptors in GH(3)MORDOR cells to a density similar to that of delta-opioid receptors in the GH(3)DOR clone resulted in abolishment of coupling to Ca(2+) channels, but not to adenylyl cyclase. Furthermore, although significantly greater amounts of all G proteins were activated by delta-opioid receptors in GH(3)MORDOR cells, delta-opioid receptor activation in GH(3)DOR cells resulted in coupling to the identical pattern of G proteins seen in GH(3)MORDOR cells. These findings suggest that different threshold densities of delta-opioid receptors are required to activate critical amounts of G proteins needed to produce coupling to specific effectors and that delta-opioid receptors couple more efficiently to adenylyl cyclase than to L-type Ca(2+) channels.
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Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA. pratherpaull@exchange.uams.edu
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D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000477:Alkylating Agents / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000378:metabolism / Q000502:physiology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D005283:Fentanyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000096:biosynthesis / Q000502:physiology; D007473:Ion Channels / Q000502:physiology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017465:Receptors, Opioid, delta / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000477:Alkylating Agents; D000701:Analgesics, Opioid; D020746:Calcium Channels, L-Type; D007473:Ion Channels; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D010566:Virulence Factors, Bordetella; C046222:3-methylfentanyl isothiocyanate; D001464:Barium; D009271:Naltrexone; C024524:beta-funaltrexamine; D020881:Enkephalin, D-Penicillamine (2,5)-; D020962:Heterotrimeric GTP-Binding Proteins; D000262:Adenylyl Cyclases; D005283:Fentanyl