title: Localization of filamin in smooth muscle.
abstract: The distribution of contractile and cytoskeletal proteins in smooth muscle has been mapped by immunocytochemical methods, with special reference to the localization of the actin-binding protein, filamin. Immunolabeling of ultrathin sections of polyvinylalcohol-embedded smooth muscle distinguished two domains in the smooth muscle cell: (a) actomyosin domains, made up of continuous longitudinal arrays of actin and myosin filaments, and (b) longitudinal, fibrillar, intermediate filament domains, free of myosin but containing actin and alpha-actinin-rich dense bodies. Filamin was found to be localized specifically in the latter intermediate filament-actin domains, but was excluded from the core of the dense bodies. Filamin was also localized close to the cell border at the inner surface of the plasmalemma-associated plaques. In isolated cells the surface filamin label showed a rib-like distribution similar to that displayed by vinculin. It is speculated that the two domains distinguished in these studies may reflect the existence of two functionally distinct systems: an actomyosin system required for contraction and an intermediate filament-actin system, with associated gelation proteins, that is responsible, at least in part, for the slow relaxation and tone peculiar to smooth muscle.
mesh_terms: D000818:Animals; D002645:Chickens; D003285:Contractile Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000648:ultrastructure; D064448:Filamins; D005455:Fluorescent Antibody Technique; D005895:Gizzard, Avian / Q000648:ultrastructure; D006168:Guinea Pigs; D007158:Immunologic Techniques; D007382:Intermediate Filaments / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000648:ultrastructure; D009124:Muscle Proteins / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism / Q000648:ultrastructure*; D013552:Swine
chemical_list: D003285:Contractile Proteins; D064448:Filamins; D008840:Microfilament Proteins; D009124:Muscle Proteins