Fig. 4.

Evidence suggesting a G_s linkage for the CB1 receptor. A, CHO-hCB1 cells were treated overnight with pertussis toxin. HU210 did not affect basal levels of cAMP accumulation in the absence of forskolin. Increasing concentrations of forskolin resulted in an amplification of HU210-induced cAMP accumulation above forskolin levels. Data are mean ± SEM from a representative experiment. B, cAMP levels after pretreatment with cholera toxin. Cholera toxin results in an increase in basal cAMP accumulation. HU210 stimulation in the absence of forskolin resulted in a U-shaped concentration response curve, with inhibition at lower doses but stimulation at high doses. Data are mean ± SEM from a representative experiment.C, Cells were treated overnight with pertussis toxin before treatment with cholera toxin. An amplified signal was observed after cholera toxin treatment (+PTX/CTX), compared with pertussis treatment (+PTX) alone. All experiments were performed in the absence of forskolin. Data are mean ± SEM from a representative experiment.