A role for the tyrosine kinase Pyk2 in depolarization‐induced contraction of vascular smooth muscle (609.3)

Background: Depolarization of vascular smooth muscle induces rapid (phasic) contraction followed by sustained (tonic) contraction. The latter is due to activation of the RhoA/Rho‐kinase pathway via genistein‐sensitive tyrosine phosphorylation. Objective: To determine if the Ca2 + ‐dependent tyrosine kinase Pyk2 is involved in depolarization‐induced sustained contraction. Methods: Depolarization of endothelium‐free rat caudal arterial smooth muscle was induced by high extracellular [K + ] in the absence or presence of Pyk2 inhibitors. Isometric force was measured with a force transducer and Pyk2 activation (autophosphorylation of Y402) was quantified by western blotting with phosphospecific antibodies. Results: Depolarization induced Pyk2‐Y402 phosphorylation in a time‐dependent manner. Pyk2 inhibitors (sodium salicylate, PF431396 and others) prevented Y402 phosphorylation and inhibited K+‐induced contraction. Vanadate (tyrosine phosphatase inhibitor)‐, but not calyculin A (Ser/Thr phosphatase inhibitor)‐induced contraction was also inhibited by Pyk2 inhibition. Conclusion: Membrane depolarization induces phosphorylation and activation of Pyk2, which is required for the tonic phase of K+‐induced contraction.