FXYD3 facilitates Na 1 and liquid absorption across human airway epithelia by increasing the transport capacity of the Na/K ATPase

Na/K ATPase activity is essential for ion transport across epithelia. FXYD3, a y subunit of the Na/K ATPase, is expressed in the airway, but its function remains undetermined. Single-cell RNA sequencing and immunohistochemistry revealed that FXYD3 localizes within the basolateral membrane of all airway epithelial cells. To study FXYD3 function, we reduced FXYD3 expression using siRNA. After permeabilizing the apical membrane with nystatin, epithelia pretreated with FXYD3-targeting siRNA had lower ouabain-sensitive short-circuit currents than control epithelia. FXYD3-targeting siRNA also reduced amiloride-sensitive short-cir-cuit currents and liquid absorption across intact epithelia. These data are consistent with FXYD3 facilitating Na+ and liquid absorption. FXYD3 may be needed to maintain the high rates of Na + and fluid absorption observed for airway and other FXYD3-expressing epithelia.