Down-regulation of cannabinoid receptor agonist-stimulated [ [formula omitted]]GTPγS binding in synaptic plasma membrane from chronic ethanol exposed mouse

Abstract

In our previous study, we demonstrated that chronic ethanol (EtOH) exposure down-regulated the cannabinoid receptors (CB1) in mouse brain synaptic plasma membrane (SPM) (Basavarajappa et al., Brain Res. 793 (1998) 212–218). In the present study, we investigated the effect of chronic EtOH (4-day inhalation) on the CB1 agonist stimulated guanosine-5′- O-(3-[ 35 S ]thio)-triphosphate ([ 35 S ]GTPγS) binding in SPM from mouse. Our results indicate that the net CP55,940 stimulated [ 35 S ]GTPγS binding was increased with increasing concentrations of CP55,940 and GDP. This net CP55,940 (1.5 μM) stimulated [ 35 S ]GTPγS binding was reduced significantly (−25%) in SPM from chronic EtOH group (175±5.25%, control; 150±8.14%, EtOH; P<0.05). This effect occurs without any significant changes on basal [ 35 S ]GTPγS binding (152.1±10.7 for control, 147.4±5.0 fmol/mg protein for chronic EtOH group, P>0.05). Non-linear regression analysis of net CP55,940 stimulated [ 35 S ]GTPγS binding in SPM showed that the B max of cannabinoid stimulated binding was significantly reduced in chronic EtOH exposed mouse ( B max=7.58±0.22 for control; 6.42±0.20 pmol/mg protein for EtOH group; P<0.05) without any significant changes in the G-protein affinity ( K d=2.68±0.24 for control; 3.42±0.31 nM for EtOH group; P>0.05). The pharmacological specificity of CP55,940 stimulated [ 35 S ]GTPγS binding in SPM was examined with CB1 receptor antagonist, SR141716A and these studies indicated that CP55,940 stimulated [ 35 S ]GTPγS binding was blocked by SR141716A with a decrease ( P<0.05) in the IC 50 values in the SPM from chronic EtOH group. These results suggest that the observed down-regulation of CB1 receptors by chronic EtOH has a profound effect on desensitization of cannabinoid-activated signal transduction and possible involvement of CB1 receptors in EtOH tolerance and dependence.