Question

How can you experimentally demonstrate that a specific GPCR couples through Gi alpha subunit to inhibit adenylyl cyclase activity

Answer 1

When a GPCR  binds a ligand, the ligand triggers a conformational change in the seven-transmembrane region of the receptor. This activates the C-terminus, whichb then recruits a substance that in turn activates  the G protein associated with the GPCR.Activation of  GPCRs cause a conformational change in the attached G protein  complex, which results in the Gs alpha subunit's exchanging GDP for GTP and separation from the beta and gamma subunits. The Gs alpha subunit, in turn, activates the G protein associated with the GPCR.Activation , which quickly converts ATP into cAMP. Experimentally the Gs-selective (R,R)- and the Gs- and Gi-activating (R,S)-fenoterol to selectively activate β2ARs (β1AR blockade present) in combination with Gi inactivation with pertussis toxin (PTX). It also determined the effect of PTX upon basal and forskolin-mediated responses. In contrast was measured ex vivo in left ventricular strips and cAMP accumulation was measured in isolated ventricular cardiomyocytes from adult Wistar rats.Thus giving experimentally demonstration that a specific GPCR couples through Gi alpha subunit to inhibit adenylyl cyclase activity