Adult alveolar epithelial cells express multiple subtypes of voltage-gated K⁺ channels that are located in apical membrane

Whole cell perforated patchclamp experiments were performed with adult rat alveolar epithelial cells. The holding potential was -60 mV, and depolarizing voltage steps activated voltage-gated K⁺ (Kv) channels. The voltage-activated currents exhibited a mean reversal potential of -32 mV. Complete activation was achieved at -10 mV. The currents exhibited slow inactivation, with significant variability in the time course between cells. Tail current analysis revealed cell-to-cell variability in K⁺ selectivity, suggesting contributions of multiple Kv α-subunits to the whole cell current. The Kv channels also displayed steady-state inactivation when the membrane potential was held at depolarized voltages with a window current between -30 and 5 mV. Analysis of RNA isolated from these cells by RT-PCR revealed the presence of eight Kv α-subunits (Kv1.1, Kv1.3, Kv1.4, Kv2.2, Kv4.1, Kv4.2, Kv4.3, and Kv9.3), three β-subunits (Kvβ1.1, Kvβ2.1, and Kvβ3.1), and two K⁺ channel interacting protein (KChIP) isoforms (KChIP2 and KChIP3). Western blot analysis with available Kv α-subunit antibodies (Kv1.1, Kv1.3, Kv1.4, Kv4.2, and Kv4.3) showed labeling of 50-kDa proteins from alveolar epithelial cells grown in monolayer culture. Immunocytochemical analysis of cells from monolayers showed that Kv1.1, Kv1.3, Kv1.4, Kv4.2, and Kv4.3 were localized to the apical membrane. We conclude that expression of multiple Kv α-, β-, and KChIP subunits explains the variability in inactivation gating and K⁺ selectivity observed between cells and that Kv channels in the apical membrane may contribute to basal K⁺ secretion across the alveolar epithelium.