[Mechanisms of bronchial hyperreactivity. Role of smooth muscle]

The understanding of the cellular and molecular mechanisms involved in the contraction of airway smooth muscle has tremendously advanced in the recent years. Extracellular messengers that control the muscle contraction as well as both the membrane transduction processes and the activation of the contractile proteins are known in some details. Sensitization alters the contractility of airway smooth muscle. It increases shortening in the early phase of the contraction when rapidly cycling cross bridges are operative. At the molecular level, the responsible mechanism is an increment in the activity of the processes leading to phosphorylation of the myosin light chain. Such an alteration in the airway smooth muscle contractility may be observed in the early phase of the development of bronchial hyperresponsiveness.