K+-channel opening as a mechanism for relaxing airways smooth muscle.

The properties and physiological roles of K+-channels in the plasmalemma of airways smooth muscle are currently being clarified by the use of techniques such as patch-clamp recording. K+-channel activity plays an important role in determining both the resting membrane potential and the electrical excitability of the airways smooth muscle cell. Established bronchodilators such as agonists at beta-adrenoceptors and methylxanthines may provide K+-channel opening but this is not crucial for their relaxant action. The actions of other smooth muscle relaxants such as BRL 34915 and pinacidil (Fig.) may more closely depend on their ability to open K+-channels and such agents are currently being examined to determine whether they protect against bronchoconstrictor challenge in vivo or have beneficial effects in asthma.