A Calponin Peptide Enhances Ca Sensitivity of Smooth Muscle Contraction without Affecting Myosin Light Chain Phosphorylation

In permeabilized smooth muscle, exogenously applied calponin binds to myofibrils and reduces Ca -activated tension (Itoh, T., Suzuki, S., Suzuki, A., Nakamura, F., Naka, M., and Tanaka, T.(1994) Pfl ü gers Arch. Eur. J. Physiol. 427, 301 - 308). A calponin peptide (calponin Phe -Arg ), which inhibits the binding of calponin to actin, blocks the action of calponin and enhances the contraction induced by submaximal Ca in permeabilized vascular smooth muscle. Unlike calmodulin, this peptide enhances the Ca -induced contraction without a corresponding increase in the level of myosin light chain phosphorylation. These results suggest that calponin decreases the sensitivity of smooth muscle to Ca at a given level of myosin light chain phosphorylation.