TABLE 1
Characterization of stably transfected HEK cell lines
Receptor number (Bmax) and affinity (Kd) was determined by [3H]SR 141716A binding (CB1) or [3H]raclopride binding (D2) as described under Materials and Methods. Log IC50 values for the displacement of [3H]SR 141716A by CP 55,940 performed in the presence and absence of 100 nM quinpirole, and [3H]raclopride displacement by quinpirole performed in the presence and absence of 100 nM CP 55,940 are presented. The ability of the receptor activation to alter forskolin (fsk)-stimulated cAMP accumulation was determined as described under Materials and Methods. Emax values for each concentration-response curve are presented as a percentage of the total forskolin-mediated stimulation. After overnight treatment with pertussis toxin, D2-mediated inhibition was blocked in both singly and dually expressing cells, whereas a small, but significant concentration-dependent increase in cAMP accumulation was observed for both CB1-containing cell lines. Data are mean ± S.E.M. for three experiments performed in quadruplicate for cAMP assays or duplicate for binding assays.