Potassium channels and airway function: new therapeutic prospects.

Potassium (K+) channels have long been associated with recovery of excitable cells after depolarisation and drugs that block these channels, such as tetraethylammonium and 4- aminopyridine, cause an increase in excita- bility.In airway smooth muscle these K+ channel blocking drugs result in spontaneous action potentials and a reduced threshold of excitation,'2 which may be similar to the elec- trophysiological changes described in asth- matic airways.'The recent development of drugs that open K+ channels in smooth muscle has reawakened interest in potassium channels because such drugs relax airway smooth muscle and may reduce the hyperreactivity of asthma.It is now clear that there is great diversity ofK+ channels in different cells, raising the possibility that selective drugs may be developed for specific cell types, with therapeutic benefit.We review here some ofthe recent developments in under- standing K+ channels in airways and the therapeutic prospects for new K+ channel activators. Potassium channels and their typesRecent electrophysiological studies and the use of new pharmacological agents have shown that K+ channels are present on cells of several types, including nerves, secretory cells, and skeletal and smooth muscle cells.45K+ channels are now seen to be diverse and may be modulated by changes in membrane potential, ion concentration, or receptor activation.All cells in the body are likely to have K+ channels and they may have more than one type.