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. These channels play important roles in maintenance of membrane potential, control of cell volume, regulation of cell proliferation, and support of transepithelial electrolyte and nutrient transport. 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. 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. 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 Ca ²⁺ and cAMP. In this review, the diversity of K ⁺ channel expression and the functional role of these channels in transepithelial electrolyte and fluid transport in lung epithelia are addressed.