PHI-1 induced enhancement of myosin phosphorylation in chicken smooth muscle.

Herein, we provide evidence that in chicken smooth muscle, G-protein stimulation by a Rho-kinase pathway leads to an increase in myosin light chain phosphorylation. Additionally, G-protein stimulation did not increase MYPT1 phosphorylation at Thr695 or Thr850, and CPI-17, was not expressed in chicken smooth muscle. However, PHI-1 was present in chicken smooth muscle tissues. Both agonist and GTP(gamma)S stimulation result in an increase in PHI-1 phosphorylation, which is inhibited by inhibitors to both Rho-kinase (Y-27632) and (PKC) GF109203x. These data suggest that PHI-1 may act as a CPI-17 analog in chicken smooth muscle and inhibit myosin phosphatase activity during G-protein stimulation to produce Ca2+ sensitization.