Opioid and cannabinoid receptors share a common pool of GTP-binding proteins in cotransfected cells, but not in cells which endogenously coexpress the receptors.
1. Opioid (mu, delta, kappa) and cannabinoid (CB1, CB2) receptors are coupled mainly to Gi/Go GTP-binding proteins. The goal of the present study was to determine whether different subtypes of opioid and cannabinoid receptors, when coexpressed in the same cell, share a common reservoir, or utilize different pools, of G proteins. 2. The stimulation of [35S]GTPgammaS binding by selective opioid and cannabinoid agonists was tested in transiently transfected COS-7 cells, as well as in neuroblastoma cell lines. In COS-7 cells, cotransfection of mu- and delta-opioid receptors led to stimulation of [35S]GTPgammaS binding by either mu-selective (DAMGO) or delta-selective (DPDPE) agonists. The combined effect of the two agonists was similar to the effect of either DAMGO or DPDPE alone, suggesting the activation of a common G-protein reservoir by the two receptor subtypes. 3. The same phenomenon was observed when COS-7 cells were cotransfected with CB1 cannabinoid receptors and either mu- or delta-opioid receptors. 4. On the other hand, in N18TG2 neuroblastoma cells, which endogenously coexpress CB1 and delta-opioid receptors, as well as in SK-N-SH neuroblastoma cells, which coexpress mu- and delta-opioid receptors, the combined effects of the various agonists (the selective cannabinoid DALN and the selective opioids DPDPE and DAMGO) were additive, implying the activation of different pools of G proteins by each receptor subtype. 5. These results suggest a fundamental difference between native and artificially transfected cells regarding the compartmentalization of receptors and GTP-binding proteins.
Shapira
M
M
Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Israel.
Vogel
Z
Z
Sarne
Y
Y
D000700:Analgesics / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D005048:Etorphine / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D009447:Neuroblastoma; D010617:Phenanthridines / Q000494:pharmacology; D011869:Radioligand Assay; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000235:genetics* / Q000378:metabolism*; D011957:Receptors, Opioid / Q000235:genetics* / Q000378:metabolism*; D017465:Receptors, Opioid, delta / Q000235:genetics / Q000378:metabolism; D017473:Receptors, Opioid, kappa / Q000235:genetics / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013462:Sulfur Radioisotopes; D014162:Transfection; D014407:Tumor Cells, Cultured
D000700:Analgesics; D000701:Analgesics, Opioid; D010617:Phenanthridines; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D013462:Sulfur Radioisotopes; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D005048:Etorphine; C032426:desacetylnantradol; D020881:Enkephalin, D-Penicillamine (2,5)-; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins