Cellular and molecular neurobiology
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Cell. Mol. Neurobiol. · Jun 2000
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 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.