What kinds of signals are perceived by vascular smooth muscles, including physical factors?

Contraction kinetics of smooth-muscle preparations (rat portal vein, rat tracheal muscle) were studied by means of force-velocity relations obtained from after-loaded isotonic contractions or from the analysis of the isometric tension increase. Furthermore, the time constant of the tension recovery following an inhibiting length vibration reflected the contraction kinetics as well. Signals that induce changes in the calcium concentration or the area of overlap between actin and myosin cause changes mainly in the number of acting cross-bridges. Decrease in temperature, pH reduction, and a long-term stimulation induce slower contraction kinetics probably because of a lesser myosin light-chain kinase activity. The results obtained give further evidence for different mechanisms controlling extent and rate of smooth-muscle contraction.