Regulation of G Protein Signals by Membrane Domains

Caveolae are membrane domains having caveolin‐1 (Cav‐1) or caveolin‐3 (Cav‐3) as their main structural component. To determine whether caveolae could affect Ca 2+ signaling through the Gα q /phospholipase Cβ (PLCβ) pathway, we studied Gα q and Gβγ interactions in Fischer Rat Thyroid cells that lack Cav‐1 (FRTcav − ) and a Cav‐1 stable transfection line (FRTcav + ) that forms caveolae‐like domains. We find that eCFP‐Gβγ and Gα q ‐eYFP are closely associated in both cell lines. Upon stimulation, Gα q ‐eYFP and eCFP‐Gβγ association remains high in FRTcav − cells, but decreases completely in FRTcav + cells suggesting that Cav‐1 is increasing the separation between Gα q ‐Gβγ subunits. In FRTcav − cells, a rapid recovery of calcium is observed after stimulation, but FRTcav + cells show a sustained elevated Ca 2+ level. Fluorescence studies show specific interactions between Gα q and Cav‐1 that increase upon stimulation, and that the mobility of eGFP‐Gβγ in FRTcav + cells, but not FRTcav‐ cells, increases greatly with stimulation. These results suggest that activation allows Gα q to switch association from Gβγ to Cav‐1 releasing Gβγ from caveolae and prolonging the heterotrimer recombination time. In cardiac myocytes, stimulation by carbachol causes a loss in co‐localization between Cav‐3 and Gβ1 suggesting that this mechanism may be responsible for prolonged Ca 2+ signals in these cells.