Mechanotransduction through fibronectin-integrin focal adhesion in microvascular smooth muscle cells: is calcium essential?

Am J Physiol Heart Circ Physiol. 2012 May 15;302(10):H1965-73. doi: 10.1152/ajpheart.00598.2011. Epub 2012 Mar 16.

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+).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amides / pharmacology
  • Animals
  • Arterioles / cytology
  • Arterioles / physiology
  • Calcium / metabolism*
  • Calcium Signaling / physiology
  • Cells, Cultured
  • Collagen Type I / physiology
  • Collagen Type IV / physiology
  • Fibronectins / physiology*
  • Focal Adhesions / physiology*
  • Integrins / physiology*
  • Mechanotransduction, Cellular / physiology*
  • Microscopy, Atomic Force
  • Microscopy, Confocal
  • Microspheres
  • Models, Animal
  • Muscle, Smooth, Vascular / cytology*
  • Muscle, Smooth, Vascular / physiology*
  • Pyridines / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • rho-Associated Kinases / antagonists & inhibitors

Substances

  • Amides
  • Collagen Type I
  • Collagen Type IV
  • Fibronectins
  • Integrins
  • Pyridines
  • Y 27632
  • rho-Associated Kinases
  • Calcium