Abstract
Actin was found to be the major source of myofibrillar protein heterogeneity in smooth muscles. Three isoelectric variants, alpha-smooth muscle (alpha-SM), beta-non-muscle (beta-NM), and gamma-actins (gamma-SM and gamma-NM) were measured in 15 different smooth muscles, alpha-SM and gamma-actin contents displayed an inverse relationship in a given smooth muscle, some of which contained primarily alpha-SM actin while gamma-actins dominated in others. alpha-SM actin and gamma-actin distributions were tissue-specific, independent of species. A greater proportion of alpha-SM actin appears to be associated with tissues having a high degree of tonic activity. beta-Nonmuscle actin was a significant, and relatively constant, component of all smooth muscle tissues. The high NM-actin content of these tissues may reflect the importance of proliferative, synthetic, or secretory activities in smooth muscle, because the alpha-SM actin disappeared in tissue culture with a time course paralleling the modulation of phenotype from a contractile to a proliferative cell. Two tropomyosin subunits were present in approximately equal amounts in all smooth muscle tissues studied. One tropomyosin subunit exhibited identical mobility on two-dimensional gel electrophoresis, while the other was characterized by some species-specific variation which was unrelated to actin variant distribution. No variants of the 20,000-dalton regulatory light chain of myosin were observed. These results suggest that SM-specific actin variants are associated with functional diversity among smooth muscles.
Highlights
Actin was found to be the major souorcfemyofibril- iants specific to smooth muscle (a-SM’and y-SM actin) plus lar proteinheterogeneityin smooth muscles
Three appreciable amounts of the two cytoplasmic actins found in isoelectric variants, a-smooth muscle (a-SM), 8-non- virtuallyalleukaryotic cells (P-NM and y-NM actin)
The muscle (8-NM), and y-actins (y-SM and y-NM) were possible relationship of actin variants to smootmhuscle funcmeasured in 15 different smooth muscles. a-SM and y- tion is notknown. actin contents displayed an inverse relationship in a The aimof this study was to determine whether the distrigiven smoothmuscle, some of which containedprimar- bution of actin variants and/or the presence of myosin light ily a-SM actin while y-actins dominated in others. a- chainor tropomyosin subunitvariantsis associatedwith
Summary
One tropomyosin subunit exhibited identical mosmooth muscle layers relatively free of nonmuscle cells which would bias contractile protein measurements; 2) availability of mechanical data and/or estimates of total actin, tropomyosin, and myosin contents; and 3) variety, allowing species- and tissue-specific comparisons. Myosin variants exhibit differences in Isolated Smooth Muscle Cell.s“Smooth muscle layers from swine specific ATPase activity in striated muscles which are pro- aorta were aseptically dissected from the tissues. Cells were plated at a density of 5 X IO4 cells/cm for culture and grown in “199 medium (Gibco) containing 10% fetal tropomyosin subunits have been observed between fast calf serum (Gibco), 100 units/ml of penicillin and 100 pg/ml of and slow striated muscles (Cummins and Perry, 1973, 1974; Johnson, 1974), the biological significance of this is unknown. Four forms of actin have been detected in several smooth muscle tissues
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
