The effect of an acidic extracellular milieu on pH_i in phagocytosing neutrophils.

Isolated human peripheral blood neutrophils (4 replicates from 8 healthy donors) were exposed to opsonized heat-killed E coli(pathogen-to-phagocyte ratio 20:1) in standard HCO$3−$-buffered RPMI medium (pH 7.45) and a bicarbonate-free HEPES-buffered medium (pH 5.8). pH_i was monitored during bacterial ingestion. Cytosolic acidification was significantly greater following phagocytosis in the acidic extracellular medium (P < .001 by 2-way ANOVA). All data mean ± SEM.