Modulation by GM1 ganglioside of β₁-adrenergic receptor-induced cyclic AMP formation in Sf9 cells

The effect of ganglioside GM1 on isoproterenol-induced cAMP accumulation was studied in insect Sf9 cells expressing the human β₁t-adrenergic receptor by infection with recombinant baculovirus. When such Sf9 cells were treated with isoproterenol plus IBMX, intracellular cAMP formation increased approximately 10-fold over the basal level. Preincubation of the baculovirus-infected cells with GM1 for 1 h caused a concentration-dependent inhibition of the isoproterenol-induced CAMP accumulation. Phosphatidylserine, GM3, GTIb and a bovine brain ganglioside preparation lacking GM1 did not cause significant inhibition. Forskolin-induced CAMP accumulation was not affected by the GM1 treatment. Inhibition of isoproterenol-induced cAMP formation by GM1 was not observed in Sf9 cells expressing, β₂-adrenergic receptor instead of the β₁-adrenergic receptor. Binding studies with (-)-[³H]CGP12177 showed that preincubation with GM1 significantly reduced the affinity of antagonist binding to the β₁-adrenergic receptor. These results suggest that GM1 or related ganglioside structure(s) may function as natural modulator(s) of the /3,-adrenergic receptor.