title: Nonmuscle myosin II is responsible for maintaining endothelial cell basal tone and stress fiber integrity.
abstract: Cultured confluent endothelial cells exhibit stable basal isometric tone associated with constitutive myosin II regulatory light chain (RLC) phosphorylation. Thrombin treatment causes a rapid increase in isometric tension concomitant with myosin II RLC phosphorylation, actin polymerization, and stress fiber reorganization while inhibitors of myosin light chain kinase (MLCK) and Rho-kinase prevent these responses. These findings suggest a central role for myosin II in the regulation of endothelial cell tension. The present studies examine the effects of blebbistatin, a specific inhibitor of myosin II activity, on basal tone and thrombin-induced tension development. Although blebbistatin treatment abolished basal tension, this was accompanied by an increase in myosin II RLC phosphorylation. The increase in RLC phosphorylation was Ca(2+) dependent and mediated by MLCK. Similarly, blebbistatin inhibited thrombin-induced tension without interfering with the increase in RLC phosphorylation or in F-actin polymerization. Blebbistatin did prevent myosin II filament incorporation and association with polymerizing or reorganized actin filaments leading to the disappearance of stress fibers. Thus the inhibitory effects of blebbistatin on basal tone and induced tension are consistent with a requirement for myosin II activity to maintain stress fiber integrity.
authors.affiliation: Department of Neurobiology and Anatomy, West Virginia University School of Medicine, Morgantown, West Virginia 26506, USA.
authors.forename: Zoe M
authors.initials: ZM
authors.lastname: Goeckeler
authors.forename: Paul C
authors.initials: PC
authors.lastname: Bridgman
authors.forename: Robert B
authors.initials: RB
authors.lastname: Wysolmerski
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure*; D004730:Endothelium, Vascular / Q000166:cytology; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D024462:Myosin Type II / Q000037:antagonists & inhibitors / Q000378:metabolism*; D022502:Stress Fibers / Q000502:physiology*
chemical_list: D000199:Actins; D006576:Heterocyclic Compounds, 4 or More Rings; C472645:blebbistatin; D024462:Myosin Type II