Fig. 1. Myosin activity during cell spreading with and without STA and KT. During cell spreading, 30-40% of the myosin RLC was phosphorylated at a steady level for 1 hour and the RLC was further phosphorylated at 2 hours after spreading even without serum (•). The specific RLC kinase inhibitor KT (1 µM) reduced the amount of the phosphorylated RLC to less than 10% of the total RLC for 30 minutes after re-plating (). The relatively nonspecific kinase inhibitor STA (100 nM) () suppressed the RLC phosphorylation to less than 5% for a much longer period (2 hours) compared with KT. The quantitative level of RLC phosphorylation (A) was detected by modified western blots (B). Data represent the averaged value of at least three independent experiments (A). U, 1P and 2P indicate unphosphorylated, mono-phosphorylated and di-phosphorylated myosin light chains respectively (B).