TY - JOUR T1 - Alterations in Detergent Solubility of Heterotrimeric G Proteins after Chronic Activation of G<sub>i/o</sub>-Coupled Receptors: Changes in Detergent Solubility Are in Correlation with Onset of Adenylyl Cyclase Superactivation JF - Molecular Pharmacology JO - Mol Pharmacol SP - 820 LP - 825 DO - 10.1124/mol.57.4.820 VL - 57 IS - 4 AU - Michael L. Bayewitch AU - Igal Nevo AU - Tomer Avidor-Reiss AU - Rivka Levy AU - William F. Simonds AU - Zvi Vogel Y1 - 2000/04/01 UR - http://molpharm.aspetjournals.org/content/57/4/820.abstract N2 - Prolonged Gi/o protein-coupled receptor activation has been shown to lead to receptor internalization and receptor desensitization. In addition, it is well established that although acute activation of these receptors leads to inhibition of adenylyl cyclase (AC), long-term activation results in increased AC activity (especially evident on removal of the inhibitory agonist), a phenomenon defined as AC superactivation or sensitization. Herein, we show that chronic exposure to agonists of Gi-coupled receptors also leads to a decrease in cholate detergent solubility of G protein subunits, and that antagonist treatment after such chronic agonist exposure leads to a time-dependent reversal of the cholate insolubility. With Chinese hamster ovary and COS cells transfected with several Gi/o-coupled receptors (i.e., μ- and κ-opioid, and m4-muscarinic), we observed that although no overall change occurred in total content of Gαi- and β1-subunits, chronic agonist treatment led to a marked reduction in the ability of 1% cholate to solubilize Gβγ as well as Gαi. This solubility shift is exclusively observed with Gαi, and was not seen with Gαs. The disappearance and reappearance of Gαi and Gβγ subunits from and to the detergent-soluble fractions occur with similar time courses as observed for the onset and disappearance of AC superactivation. Lastly, pertussis toxin, which blocks acute and chronic agonist-induced AC inhibition and superactivation, also blocks the shift in detergent solubility. These results suggest a correlation between the solubility shift of the heterotrimeric Gi protein and the generation of AC superactivation. ER -