Volume changes in activated human neutrophils: the role of Na+/H+ exchange

The apparent volume of neutrophils, as measured electronically with the Coulter counter, has been reported to increase upon treatment with chemotactic factors. The occurrence of a volume change was confirmed by forward angle light scattering and by isotopic measurements of intracellular water space in cells treated with 12-O-tetradecanoylphorbol 13,acetate (TPA) or formyl-methionyl-leucyl-phenylalanine (FMLP). Cell swelling was associated with an increase in the osmotic content of the cells, determined from Boyle-van't Hoff plots, and with an increase in Na+ content, measured by flame photometry. The volume change was inhibited by replacement of extracellular Na+ with K+ or N-methyl-D-glucamine+, or by addition of amiloride. Swelling was also inhibited by the 5-N-substituted analogs of amiloride, which are potent specific inhibitors of the Na+/H+ antiport. This pathway is activated in neutrophils by both TPA and FMLP. Activation of Na+/H+ exchange, determined as a Na+ -dependent and amiloride-sensitive cytoplasmic alkalinization, was also found when neutrophils were treated with hypertonic solutions. The hypertonic activation of the antiport was similarly followed by cell swelling, detectable by electronic sizing. The results indicate that activation of Na+/H+ exchange can lead to significant cell swelling in neutrophils.