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 det ermine the expression of voltage-dependent potassium channel currents and mRNAs in human airway smooth muscle cells, and tension measurement s were used to examine the functional role of specific potassium chann el gene products in human bronchial smooth muscle, RNA from airway smo oth muscle tissue revealed the presence of Kv1.2 (11 kilobases (kb)) a nd 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 react ion from cultured human myocytes confirmed that the identified transcr ipts were expressed by smooth muscle cells, The available voltage-depe ndent potassium current in human airway myocytes was insensitive to ch arybdotoxin (200 nM) but blocked by 4-aminopyridine. Dendrotoxin (1-30 0 nM; inhibits Kv1.1 and Kv1.2 channels), charybdotoxin (10 nM to 1 mu M; inhibits K-Ca, and Kv1.2 channels), and glybenclamide (0.1-100 mu M; inhibits K-ATP channels) had no effect on resting tone, Conversely, 4-aminopyridine increased resting tension with an EC(50) (1.8 mM) equ ivalent to that observed for current inhibition (1.9 mM). Human airway myocytes express mRNA from several members of the Kv1 gene family; th e channel that underlies the predominate voltage dependent current and the regulation of basal tone appears to be Kv1.5.