Airway hyperreactivity, smooth muscle and calcium.

One suggested cause of airway hyperreactivity is a change in the excitation-contraction coupling of airway smooth muscle cells, leading to a non-specific supersensitivity to chemically distinct and pharmacologically unrelated agents. As the concentration of intracellular, free calcium determines the degree of contractile activity, the increase in intracellular calcium evoked by a given stimulus may be larger than normal 1) if the delivery of calcium to the myoplasm is increased, either this is caused by an increased inflow from the extracellular medium or by increased release from intracellular stores, 2) if removal of calcium from the contractile proteins is reduced, either by inhibition of uptake by intracellular stores or of active extrusion from the cell, 3) if the effect of a given increase in intracellular calcium concentration causes a greater than normal degree of activation of the contractile proteins. It cannot be excluded that changes in one or more of these mechanisms, induced by mediators, hormones, or other agents may be a contribution factor to airway hyperreactivity.