MOLECULAR-IDENTIFICATION OF THE ROLE OF VOLTAGE-GATED K-POTENTIAL IN RAT PULMONARY-ARTERY MYOCYTES( CHANNELS, KV1.5 AND KV2.1, IN HYPOXIC PULMONARY VASOCONSTRICTION AND CONTROL OF RESTING MEMBRANE)

Hypoxia initiates pulmonary vasoconstriction (HPV) by inhibiting one o r more voltage-gated potassium channels (Kv) in the pulmonary artery s mooth muscle cells (PASMCs) of resistance arteries, The resulting memb rane depolarization increases opening of voltage-gated calcium channel s, raising cytosolic Ca2+ and initiating HPV. There are presently nine families of Ky channels known and pharmacological inhibitors lack the specificity to distinguish those involved in control of resting membr ane potential (E-m) or HPV. However, the Ky channels involved in E-m a nd HPV have characteristic electrophysiological and pharmacological pr operties which suggest their molecular identity, They are slowly inact ivating, delayed rectifier currents, inhibited by 4-aminopyridine (4-A P) but insensitive to charybdotoxin. Candidate Ky channels with these traits (Kv1.5 and Kv2.1) were studied. Antibodies were used to immunol ocalize and functionally characterize the contribution of Kv1.5 and Kv 2.1 to PASMC electrophysiology and vascular tone. Immunoblotting confi rmed the presence of Kv1.1, 1.2, 1.3, 1.5, 1.6, and 2.1, but not Kv1.4 , in PASMCs, Intracellular administration of anti-Kv2.1 inhibited whol e cell K+ current (I-K) and depolarized E-m, Anti-Kv2.1 also elevated resting tension and diminished 4-AP-induced vasoconstriction in membra ne-permeabilized pulmonary artery rings, Anti-Kv1.5 inhibited I-K and selectively reduced the rise in [Ca2+](i) and constriction caused by h ypoxia and 4-AP, However, anti-Kv1.5 neither caused depolarization nor elevated basal pulmonary artery tone. This study demonstrates that an tibodies can be used to dissect the whole cell K+ currents in mammalia n cells, We conclude that Kv2.1 is an important determinant of resting E-m in PASMCs from resistance arteries. Both Kv2.1 and Kv1.5 contribu te to the initiation of HPV.