Ion Transport: Potassium Channels

Airway and alveolar epithelial cells express a variety of K+ channels that are specifically localized to either the apical or basolateral membrane depending upon their physiological function (Halm, 2016; Hollenhorst et al., 2011). These channels play important roles in maintenance of membrane potential, control of cell volume, regulation of cell proliferation, and support of transepithelial electrolyte transport (Bardou et al., 2009). K+ channels present in the apical membrane of alveolar epithelial cells, for example, facilitate K+ secretion, thus contributing to the elevated K+ concentration observed in alveolar fluid (Lee et al., 2003; O’Grady and Lee, 2003). K+ channels localized to the basolateral membrane of airway epithelial cells contribute to transepithelial electrolyte and fluid transport by sustaining the electrical driving force necessary for anion efflux or cation influx and limit fluctuations in intracellular K+ concentration associated with changes in Na+-K+ ATPase activity (Cotton, 2000; McCann and Welsh, 1990). Signaling molecules that control the absorptive and secretory functions of lung epithelia have been shown to regulate specific K+ channel subtypes through the mobilization of intracellular second messengers such as Ca2+ and cAMP (MacVinish et al., 1998; Mall et al., 2000). In this review, the diversity of K+ channel expression and the functional roles of these channels in lung epithelia are discussed.