title: Mechanotransduction through fibronectin-integrin focal adhesion in microvascular smooth muscle cells: is calcium essential?
abstract: It is believed that increased transmural pressure exerts force on vascular smooth muscle cells (VSMCs) and triggers Ca(2+) signaling as an initiating event responsible for the arteriolar myogenic response. However, the mechanisms linking the pressure increase to Ca(2+) signaling are unclear. We have shown previously using atomic force microscopy (AFM) that mechanical force induces a VSMC contractile response when applied to single fibronectin (FN; Sun Z, Martinez-Lemus LA, Hill MA, Meininger GA. Am J Physiol Cell Physiol 295; C268-C278, 2008) focal adhesion sites. This current study seeks to determine whether application of force to single focal adhesions can cause a change in VSMC Ca(2+). Experiments were performed in low passage (p3∼10) as well as in freshly isolated skeletal muscle arteriole VSMCs. AFM-attached microbeads (5 μm) were coated with FN or collagen type I (CN-I) or type IV (CN-IV) and placed on a VSMC for 20 min, resulting in formation of a focal adhesion between the cell and the microbead. In low passage VSMCs, mechanically pulling on the FN-coated beads (800∼3000 pN) did not induce a Ca(2+) increase but did cause a contractile response. In freshly isolated VSMCs, application of an FN or CN-I-coated bead onto the cell surface induced global Ca(2+) increases. However, these Ca(2+) increases were not correlated with the application of AFM pulling force to the bead or with the VSMC contractile responses to FN-coupled pulling. Chelating cytosolic Ca(2+) using BAPTA loading had no negative effect on the focal adhesion-related contractile response in both freshly isolated and low passage VSMCs, while the Rho-kinase inhibitor Y27632 abolished the micromyogenic response in both cases. These observations suggest that, in freshly isolated and cultured VSMCs, application of mechanical force to a focal adhesion does not invoke an acute global Ca(2+) increase. On the other hand, our data support a role for Rho-linked signaling mechanism involved in mechanotransduction leading to focal contraction that is independent of the need for a global increase in VSMC Ca(2+).
authors.affiliation: Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211, USA. sunzh@missouri.edu
authors.forename: Zhe
authors.initials: Z
authors.lastname: Sun
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Li
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Meininger
mesh_terms: D000577:Amides / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000166:cytology / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D024042:Collagen Type I / Q000502:physiology; D024141:Collagen Type IV / Q000502:physiology; D005353:Fibronectins / Q000502:physiology*; D022001:Focal Adhesions / Q000502:physiology*; D016023:Integrins / Q000502:physiology*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D018625:Microscopy, Atomic Force; D018613:Microscopy, Confocal; D008863:Microspheres; D023421:Models, Animal; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors
chemical_list: D000577:Amides; D024042:Collagen Type I; D024141:Collagen Type IV; D005353:Fibronectins; D016023:Integrins; D011725:Pyridines; C108830:Y 27632; D054460:rho-Associated Kinases; D002118:Calcium