The adhesion junctions of smooth muscle cells may be dynamically regulated during smooth muscle contraction, and this dynamic regulation may be important for the development of active tension. In the present study, the role of α-actinin during smoothmuscle contraction was evaluated in tracheal smooth muscle tissues and freshly dissociated cells. Stimulationwith acetylcholine (ACh) increased the localization of α-actinin at the membrane of freshly dissociated smooth muscle cells, and increased the amount of β1 integrin that coprecipitated with α-actinin from muscle tissue homogenates. GFP-α-actinin fusion proteins were expressed in muscle tissues and visualized in live freshly dissociated cells. GFP-α-actinin translocated to the membrane within seconds of stimulation of the cells with ACh. Expression of the integrin-binding rod domain of α-actinin in smooth muscle tissues depressed active contraction in response to ACh. Expression of the α-actinin rod domain also inhibited the translocation of endogenous aα-actinin to the membrane, and inhibited the association of endogenous α-actinin with β1-integrin in α-actinin immunoprecipitates from tissue extracts. However, the expression of αactinin rod domain peptides did not inhibit increases in myosin light chain phosphorylation or actin polymerization in response to stimulation with ACh. Results suggest that contractile stimulation of smooth muscle causes the rapid recruitment of α-actinin to α-integrin complexes at the membrane, and that the recruitment of α-actinin to integrin complexes is necessary for active tension development in smooth muscle.
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