Molecular basis and function of voltage-gated K+ channels in pulmonary arterial smooth muscle cells

K+-channel activity-mediated alteration of the membrane potential and cytoplasmic free Ca2+ concentration ([Ca2+](cyt)) is a pivotal mechanism in controlling pulmonary vasomotor tone. By using combined approaches of patch clamp, imaging fluorescent microscopy, and molecular biology, we examined the electrophysiological properties of K+ channels and the role of different K+ currents in regulating [Ca2+](cyt), and explored the molecular identification of voltage-gated K+ (K-v)- and Ca2+-activated K+ (K-Ca)-channel genes expressed in pulmonary arterial smooth muscle cells (PASMC). Two kinetically distinct K-v currents [I-K(v)], a rapidly inactivating (A-type) and a noninactivating delayed rectifier, as well as a slowly activated K-Ca current [I-K(Ca)] were identified. I-K(v) was reversibly inhibited by 4-aminopyridine (5 mM), whereas I-K(Ca), was significantly inhibited by charybdotoxin (10-20 nM). K+ channels are composed of pore-forming alpha-subunits and auxiliary beta-subunits. Five K-v-channel alpha-subunit genes from the Shaker subfamily (K(v)1.1, K(v)1.2, K(v)1.4, K(v)1.5, and K(v)1.6), a K-v-channel alpha-subunit gene from the Shab subfamily (K(v)2.1), a K-v-channel modulatory alpha-subunit (K(v)9.3), and a K-Ca-channel alpha-subunit gene (rSLo), as well as three K-v-channel beta-subunit genes (K-v beta 1.1, K-v beta 2 and K-v beta 3) are expressed in PASMC. The data suggest that 1) native K+ channels in PASMC are encoded by multiple genes; 2) the delayed rectifier I-K(v) may be generated by the K(v)1.1, K(v)1.2, K(v)1.5, K(v)1.6, K(v)2.1, and/or K(v)2.1/K(v)9.3 channels; 3) the A-type I-K(v) may be generated by the K(v)1.4 channel and/or the delayed rectifier K-v channels (K(v)1 subfamily) associated with beta-subunits; and 4) the I-K(Ca) may be generated by the rSlo gene product. The function of the K-v channels plays an important role in the regulation of membrane potential and [Ca2+](cyt) in PASMC.