Disruption of cytoskeletal integrity impairs G(i)-mediated signaling due to displacement of G(i) proteins

beta 1 integrins play a crucial role as cytoskeletal anchorage proteins. In this study, the coupling of the cytoskeleton and intracellular signaling p athways was investigated in beta1 integrin deficient (-/-) embryonic stem c ells. Muscarinic inhibition of the L-type Ca2+ current (I-Ca) and activatio n of the acetylcholine-activated K+ current (I-K,I-ACh) was found to be abs ent in beta1 integrin(-/-) cardiomyocytes. Conversely, beta adrenoceptor-me diated modulation of I-Ca was unaffected by the absence of beta1 integrins. This defect in muscarinic signaling was due to defective G protein couplin g. This was supported by deconvolution microscopy, which demonstrated that G(i) exhibited an atypical subcellular distribution in the beta1 integrin(- /-) cardiomyocytes. A critical role of the cytoskeleton was further demonst rated using cytochalasin D, which displaced G(i) and impaired muscarinic si gnaling. We conclude that cytoskeletal integrity is required for correct lo calization and function of G(i)-associated signaling microdomains.