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1 Physiology, University of Minnesota, St. Paul, MN, USA
2 Medicine, University of Minnesota, Minneapolis, MN, USA
* To whom correspondence should be addressed. E-mail: ograd001{at}umn.edu.
Whole cell perforated patch clamp experiments were performed using adult rat alveolar epithelial cells. The holding potential was -60 mV and depolarizing voltage steps activated Kv type K+ channels. The voltage-activated currents exhibited a mean reversal potential of -32mV. 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 á 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 alpha subunits (Kv1.1, Kv1.3, Kv1.4, Kv2.2, Kv4.1, Kv4.2, Kv4.3, and Kv9.3), three beta subunits (Kv
1.1, Kv2.1, and Kv3.1), and two KChIP isoforms (KChIP2 and KChIP3). Western blot analysis with available Kv 
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 , , 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.
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