Regulation of the L-type calcium channel by alpha(5)beta(1) integrin requires signaling between focal adhesion proteins

The L-type calcium channel is the major calcium influx pathway in vascular smooth muscle and is regulated by integrin ligands, suggesting an important link between extracellular matrix and vascular tone regulation in tissue i njury and remodeling. We examined the role of integrin-linked tyrosine kina ses and focal adhesion proteins in regulation of L-type calcium current in single vascular myocytes. Soluble tyrosine kinase inhibitors blocked the in crease in current produced by alpha (5) integrin antibody or fibronectin, w hereas tyrosine phosphatase inhibition enhanced the effect. Cell dialysis w ith an antibody to focal adhesion kinase or with FRNK, the C-terminal nonca talytic domain of focal adhesion kinase, produced moderate (24 or 18%, resp ectively) inhibition of basal current but much greater inhibition (63 or 68 %, respectively) of integrin-enhanced current. A c-Src antibody and peptide inhibitors of the Src homology-2 domain or a putative Src tyrosine phospho rylation site on the channel produced similar inhibition. Antibodies to the cytoskeletal proteins paxillin and vinculin, but not a-actinin, inhibited integrin-dependent current by 65-80%. Therefore, alpha (5)beta (1). integri n appears to regulate a tyrosine phosphorylation cascade involving Src and various focal adhesion proteins that control the function of the L-type cal cium channel. This interaction may represent a novel mechanism for control of calcium influx in vascular smooth muscle and other cell types.