Enhancement of Ca 21 Influx and Ciliary Beating by Membrane Hyperpolarization due to ATP-Sensitive K 1 Channel Opening in Mouse Airway Epithelial Cells

ABSTRACT Among the several types of cells composing the airway epithelium, the ciliary cells are responsible for one of the most important defense mechanisms of the airway epithelium: the transport of inhaled particles back up into the throat by coordinated ciliary movement. Changes in the cytoplasmic Ca 21 concentration ([Ca 21 ] i ) are the main driving force controlling the ciliary activity. In mouse ciliary cells, membrane hyperpolarization from 220 to 260 mV under whole-cell voltage-clamp induced a slow but significant [Ca 21 ] i rise in a reversible manner. This rise was completely inhibited by the removal of Ca 21 from the extracellular solution. Application of diazoxide, an ATP-dependent K 1 channel opener, dose-dependently induced a membrane hyperpolarization (EC 50 5 2.3 mM), which was prevented by the addition of 5 mM glibenclamide. An inwardly rectifying current was elicited by the application of 10 mM diazoxide and suppressed by subsequent addition of 5 mM glibenclamide. Moreover, the application of 10 mM diazoxide induced a significant [Ca 21 ] i rise and facilitated ciliary movement. Multi-cell reverse-transcription polymerase chain reaction analyses and immunocytochemical staining suggested that the subunit combination of Kir6.2/SUR2B and possibly also Kir