Potassium channel activators and bronchial asthma.

The cromakalim-like KCOs relax airways smooth muscle by an action that is associated with the opening of plasmalemmal K(+)-channels. The K(+)-channel involved may be analogous to the ATP-sensitive K(+)-channel identified in pancreatic beta-cells. It is unlikely to be open under normal circumstances and plays little role in determining the strong outward rectifying behaviour of the plasmalemma of the airways smooth muscle cell. K(+)-channel opening may cause relaxation of the airways smooth muscle cell by mechanisms additional to inhibition of Ca2+ influx through L-type VOCs. The cromakalim-like KCOs have bronchodilator activity in vivo and can depress NANC excitatory neuroeffector transmission in the lung at concentrations smaller than those required to relax airways smooth muscle. The mechanism of action of cromakalim in alleviating nocturnal asthma may not involve direct relaxation of airways smooth muscle. It is possible that cromakalim may instead act to inhibit the mechanisms underlying airway hyper-reactivity.