Electrical excitability, which plays an important role in excitation-contraction coupling in the pulmonary vasculature, is regulated by transmembrane ion flux in pulmonary artery smooth muscle cells (PASMC). This study examined the heterogeneous nature of native voltage-dependent K+ channels in human PASMC. Both voltage-gated K+ (KV) currents and Ca2+-activated K+ (KCa) currents were observed and characterized. In cell-attached patches of PASMC bathed in Ca2+-containing solutions, depolarization elicited a wide range of K+ unitary conductances (6–290 pS). When cells were dialyzed with Ca2+-free and K+-containing solutions, depolarization elicited four components of KV currents in PASMC based on the kinetics of current activation and inactivation. Using RT-PCR, we detected transcripts of 1) 22 KV channel α-subunits (KV1.1–1.7, KV1.10, KV2.1, KV3.1, KV3.3–3.4, KV4.1–4.2, KV5.1, KV 6.1–6.3, KV9.1, KV9.3, KV10.1, and KV11.1), 2) three KV channel β-subunits (KVβ1–3), 3) four KCa channel α-subunits ( Slo-α1 and SK2–SK4), and 4) four KCa channel β-subunits (KCaβ1–4). Our results show that human PASMC exhibit a variety of voltage-dependent K+ currents with variable kinetics and conductances, which may result from various unique combinations of α- and β-subunits forming the native channels. Functional expression of these channels plays a critical role in the regulation of membrane potential, cytoplasmic Ca2+, and pulmonary vasomotor tone.
Functional Ion Channels in Human Pulmonary Artery Smooth Muscle Cells: Voltage-Dependent Cation Channels