Interleukin-1 Increases Vacuolar-type H-ATPase Activity in Murine Peritoneal Macrophages

Abstract Maintenance of cytoplasmic pH (pH) within a narrow physiological range is crucial to normal cellular function. This is of particular relevance to phagocytic cells within the acidic inflammatory microenvironment where the pH tends to be acid loaded. We have previously reported that a vacuolar-type H-ATPase (V-ATPase) situated in the plasma membrane of macrophages and poised to extrude protons from the cytoplasmic to the extracellular space is an important pH regulatory mechanism within the inflammatory milieu. Since this microenvironment is frequently characterized by the influx of cells known to release inflammatory cytokines, we performed studies to examine the effect of one such mediator molecule, interleukin-1 (IL-1), on pHregulation in peritoneal macrophages. IL-1 caused a time- and dose-dependent increase in macrophage pH recovery from an acute acid load. This effect was specific to IL-1 and was due to enhanced plasmalemmal V-ATPase activity. The increased V-ATPase activity by IL-1 occurred following a lag period of several hours and required de novo protein and mRNA synthesis. However, Northern blot analysis revealed that IL-1 did not exert its effect via alterations in the levels of mRNA transcripts for the A or B subunits of the V-ATPase complex. Finally, stimulation of both cAMP-dependent protein kinase and protein kinase C was required for the stimulatory effect of IL-1 on V-ATPase activity. Thus, cytokines present within the inflammatory milieu are able to modulate pH regulatory mechanisms. These data may represent a novel mechanism whereby cytokines may improve cellular function at inflammatory sites.