Depletion of focal adhesion kinase by antisense depresses contractile activation of smooth muscle.

Focal adhesion kinase (FAK) undergoes tyrosine phosphorylation in response to the contractile stimulation of tracheal smooth muscle. We hypothesized that FAK may play an important role in signaling pathways that regulate smooth muscle contraction. FAK antisense or FAK sense was introduced into muscle strips by reversible permeabilization, and strips were incubated with antisense or sense for 7 days. Antisense decreased FAK expression compared with that in untreated and sense-treated tissues, but it did not affect the expression of vinculin or myosin light chain kinase. Increases in force, intracellular free Ca2+ and myosin light chain phosphorylation in response to stimulation with ACh or KCl were depressed in FAK-depleted tissues, but FAK depletion did not affect the activation of permeabilized tracheal muscle strips with Ca2+. The tyrosine phosphorylation of paxillin, a substrate for FAK, was also significantly reduced in FAK-depleted strips. We conclude that FAK is a necessary component of the signaling pathways that regulate smooth muscle contraction and that FAK plays a role in regulating intracellular free Ca2+ and myosin light chain phosphorylation.