Alterations in smooth muscle contraction kinetics during tonic activation.

The kinetics of actin myosin interaction were studied in rat tracheal smooth muscle by analyzing the time course of post-vibration tension recovery. Longitudinal vibration (100 Hz sinus: 8% of the muscle length) of the contracted preparation (electrical field stimulation 30 Hz, 0.3 ms or 0.1 mM acetylcholine treatment) inhibits the process of force generation. The tension recovery after cessation of vibration follows a double exponential function with an initial fast and a subsequent slow component (the time constants averaged 1.17 +/- 0.10 s and 7.0 +/- 0.32 s (n = 60), respectively). Changes in the amplitude of vibration, the stimulation strength, or the extent of resting tension affect the amplitude without altering the time constants of tension recovery. These experimental conditions influence rather the number than the kinetics of acting cross-bridges. An extension of the pre-vibration stimulation period from 15 s to 16 min as well as a reduction in temperature from 37 degrees C to 25 degrees C hardly affects the extent of force development. However, the time constants of both the fast and the slow component of tension recovery were increased by up to a factor of about 7. These experimental results indicate an effect on the kinetics of actin myosin interaction.