The catalytic subunit of a H(+)/K(+) ATPase and/or Na(+)/K(+) ATPase pump which transports K(+) ions in exchange for Na(+) and/or H(+) ions across the apical membrane of epithelial cells. Uses ATP as an energy source to pump K(+) ions into the cell while transporting Na(+) and/or H(+) ions to the extracellular compartment (PubMed:9774385, PubMed:7485470, PubMed:8853415, PubMed:11341842). Involved in the maintenance of electrolyte homeostasis through K(+) ion absorption in kidney and colon (By similarity). In the airway epithelium, may play a primary role in mucus acidification regulating its viscosity and clearance (PubMed:29391451). ATP + H(+)(in) + H2O + K(+)(out) = ADP + 2 H(+)(out) + K(+)(in) + phosphate ATP + H2O + K(+)(out) + Na(+)(in) = ADP + H(+) + K(+)(in) + Na(+)(out) + phosphate The ATPase activity is regulated by monovalent cations and pH. Up-regulated by K(+) ions in a dose-dependent way. Down-regulated by Na(+) ions (PubMed:11341842). Inhibited by Na(+)/K(+)-ATPase inhibitor ouabain and H(+)/K(+)-ATPase inhibitor SCH-28080 with an intermediate sensitivity to completely resistant Na(+)/K(+)-ATPases and highly sensitive H(+)/K(+)-ATPases (PubMed:7485470, PubMed:8853415, PubMed:11341842). Optimum pH is 7.2-7.8. The ATPase pump is composed of a catalytic alpha subunit and an auxiliary non-catalytic beta subunit. The alpha subunit pairs with the beta subunit of gastric H(+)/K(+) ATPase ATP4B or the beta subunit of Na(+)/K(+) ATPases ATP1B1 and ATP1B3; this interaction is required for the formation of a functionally active pump and its targeting at the plasma membrane. Expressed in airway epithelial cells (at protein level) (PubMed:29391451). Found in skin and kidney. Detected in prostate basal cells (at protein level). Expression is increased in benign prostate hyperplasia and tumor tissues (at protein level). Up-regulated by inflammatory cytokine IL13. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IIC subfamily.