The Dynamics of Formation and Action of the Ternary Complex Revealed in Living Cells Using a G-protein-gated K+ Channel as a Biosensor

Abstract

Traditionally the consequences of activation of G-protein-coupled receptors (GPCRs) by an agonist are studied using biochemical assays. In this study we use live cells and take advantage of a G-protein-gated inwardly rectifying potassium channel (Kir3.1+3.2A) that is activated by the direct binding of Gbetagamma subunit to the channel complex to report, in real-time, using the patch clamp technique the activity of the "ternary complex" of agonist/receptor/G-protein. This analysis is further facilitated by the use of pertussis toxin-resistant fluorescent and non-fluorescent Galpha(i/o) subunits and a series of HEK293 cell lines stably expressing both channel and receptors (including the adenosine A(1) receptor, the adrenergic alpha(2A) receptor, the dopamine D(2S) receptor, the M4 muscarinic receptor, and the dimeric GABA-B(1b/2) receptor). We systematically analyzed the contribution of the various inputs to the observed kinetic response of channel activation. Our studies indicate that the combination of agonist, GPCR, and G-protein isoform uniquely specify the behavior of these channels and thus support the importance of the whole ternary complex at a kinetic level.