Velocity of translation of single actin filaments (AF) by myosin heads from antigen-sensitized airway smooth muscle.

We have previously reported increased velocity of shortening (Vo) in the sensitized airway (0.36 1o/s, +/- SE) smooth muscle compared to the control (0.26 1o/s, +/- 0.017 SE) and subsequent experiments indicated this was due to increased phosphorylation of the 20 kDa myosin light chain resulting from increased total myosin light chain kinase activity. The motility assay technique described by Kron and Spudich was employed to determine whether additionally the molecular motor (actomyosin crossbridge) itself was altered in airway smooth muscle by ragweed pollen sensitization. The motility assay measures the velocity of actin filament translation by myosin molecules. The negative results of the motility assay were valuable in determining that the pathogenesis of allergic bronchospasm is not at contractile protein level but at regulatory enzyme level.