? ? Current models of G protein-coupled receptor (GPCR) signaling cascades are often influenced by the long standing hypothesis of """"""""collision coupling"""""""" of signaling components, in which reactions result from random diffusional encounters. However, there has been much debate over whether the receptor-G protein collision or nucleotide exchange on G proteins is rate limiting in signal transduction, and physiological situations are now predicted that restrict the mobility of GPCRs. Evidence also exists for large multimolecular signaling complexes, which would have little dependence upon diffusion for effector responses. To date, examination of the role lateral diffusion of signaling components has been limited to nonspecific perturbations of the cell to modify membrane fluidity. The proposed studies present a novel technique to restrict the mobility of signaling components, and use live cell imaging and electrophysiology to test the hypothesis that lateral diffusion of GPCRs is required for signal transduction. The results of our approach will bridge emerging concepts of structure and kinetics to constrain future models of receptor-effector coupling. ? ?
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