title: Cytoskeletal targeting of calponin in differentiated, contractile smooth muscle cells of the ferret.
abstract: 1. Biochemical and quantitative image analysis methods were used to investigate the anatomical basis for the previously described agonist-induced redistribution of calponin. 2. At 140 nm resolution, the quantitative distribution of calponin in resting cells was statistically indistinguishable from that of filament bundles containing alpha-smooth muscle actin and myosin, but was significantly different from that of filaments containing beta-non-muscle actin. Conversely, in stimulated cells, the distribution of calponin was not significantly different from that of beta-actin filaments in the subplasmalemmal cell cortex but was significantly different from the distribution of alpha-actin- and myosin-containing filamentous bundles. 3. The distribution of calponin significantly differed from that of the intermediate filament proteins vimentin and desmin as well as that of the dense body protein alpha-actinin either by ratio analysis of the subcellular distribution or by colocalization analysis. 4. The imaging results, although limited to 140 nm spatial resolution, suggested the hypothesis that the agonist-induced redistribution involves the binding of calponin to isoform-specific actin filaments. This hypothesis was tested by quantifying the relative affinity of calponin for purified alpha- and beta-actin. Light scattering measurements showed that calponin induces bundle formation with beta-actin more readily than alpha-actin, indicating that calponin may be preferentially sequestered by beta-actin under appropriate conditions. 5. These results are consistent with a model whereby agonist activation decreases calponin's binding to filaments, but the tighter binding to beta-actin filaments results in a spatial redistribution of calponin to the submembranous cortex.
authors.affiliation: Cardiovascular Division, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston MA 02215, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Parker
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.forename: J X
authors.initials: JX
authors.lastname: Tang
authors.forename: T
authors.initials: T
authors.lastname: Tao
authors.forename: K G
authors.initials: KG
authors.lastname: Morgan
mesh_terms: D000199:Actins / Q000032:analysis / Q000378:metabolism; D000818:Animals; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D002454:Cell Differentiation; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005289:Ferrets; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008840:Microfilament Proteins / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D009218:Myosins / Q000032:analysis / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D011169:Portal Vein / Q000502:physiology*; D000096985:Calponins
chemical_list: D000199:Actins; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009218:Myosins; D010656:Phenylephrine; D000096985:Calponins