Migration of human polymorphonuclear leucocytes (PMNs) is dependent on cell swelling mediated by the Na+/H+ exchanger. In addition we identified an H+/K+ATPase which supports chemotaxis in a cell volume-dependent manner. The aim of the study was to identify and further characterize the functional and molecular properties of this H+/K+ATPase in PMNs and myelomonocytic HL60 cells. Western blot analysis using monoclonal antibodies against the gastric H+/K+ATPase alpha-and beta subunits yielded protein bands of the expected size. Electron microprobe analysis disclosed an ouabain-und SCH28080 sensitive Rb+-uptake mechanism and measurements of the intracellular pH regulation revealed the existence of a K+ dependent H+-extrusion mechanism sensitive to H+/K+ATPase inhibitor SCH28080. Clonig revealed the expression of the non-gastric H+/K+ATPase ATP1AL1 in HL 60 cells. Incubation of the cells with 20 mM butyrate greatly enhanced the transcription of ATP1AL1 as measured by real-time QPCR.