Expression and function of voltage-dependent potassium channel genes in human airway smooth muscle

Patch clamp and RNA-polymerase chain reaction methods were used to determine the expression of voltage-dependent potassium channel currents and mRNAs in human airway smooth muscle cells, and tension measurements were used to examine the functional role of specific potassium channel gene products in human bronchial smooth muscle. RNA from airway smooth muscle tissue revealed the presence of Kv1.2 (11 kilobases (kb)) and Kv1.5 (3.5 and 4.4 kb) transcripts, as well as Kv1.1 mRNA (9.5 kb), which has not previously been reported in smooth muscle; transcripts from other gene families were not detected. RNA-polymerase chain reaction from cultured human myocytes confirmed that the identified transcripts were expressed by smooth muscle cells. The available voltage-dependent potassium current in human airway myocytes was insensitive to charybdotoxin (200 nM) but blocked by 4-aminopyridine. Dendrotoxin (1-300 nM; inhibits Kv1.1 and Kv1.2 channels), charybdotoxin (10 nM to 1 microM; inhibits KCa and Kv1.2 channels), and glybenclamide (0.1-100 microM; inhibits KATP channels) had no effect on resting tone. Conversely, 4-aminopyridine increased resting tension with an EC50 (1.8 mM) equivalent to that observed for current inhibition (1.9 mM). Human airway myocytes express mRNA from several members of the Kv1 gene family; the channel that underlies the predominate voltage-dependent current and the regulation of basal tone appears to be Kv1.5.