A pH-stabilizing role of voltage-gated proton channels in IgE-mediated activation of human basophils

Abstract

Eosinophils and other phagocytes use NADPH oxidase to kill bacteria. Proton channels in human eosinophils and neutrophils are thought to sustain NADPH oxidase activity, and their opening is greatly enhanced by a variety of NADPH oxidase activators, including phorbol myristate acetate (PMA). In nonphagocytic cells that lack NADPH oxidase, no clear effect of PMA on proton channels has been reported. The basophil is a granulocyte that is developmentally closely related to the eosinophil but nevertheless does not express NADPH oxidase. Thus, one might expect that stimulating basophils with PMA would not affect proton currents. However, stimulation of human basophils in perforated-patch configuration with PMA, N-formyl-methionyl-leucyl-phenylalanine, or anti-IgE greatly enhanced proton currents, the latter suggesting involvement of proton channels during activation of basophils by allergens through their highly expressed IgE receptor (Fc RI). The anti-IgE-stimulated response occurred in a fraction of cells that varied among donors and was less profound than that to PMA. PKC inhibition reversed the activation of proton channels, and the proton channel response to anti-IgE or PMA persisted in Ca 2؉ -free solutions. Zn 2؉ at concentrations that inhibit proton current inhibited histamine release elicited by PMA or anti-IgE. Studied with confocal microscopy by using SNARF-AM and the shifted excitation and emission ratioing of fluorescence approach, anti-IgE produced acidification that was exacerbated in the presence of 100 M Zn 2؉ . Evidently, proton channels are active in basophils during IgE-mediated responses and prevent excessive acidification, which may account for their role in histamine release.asthma ͉ histamine ͉ patch-clamp ͉ HNVCN1 ͉ allergy

Voltage-gated proton channels maintain pH in human neutrophils during phagocytosis

“…Cells were visualized using the SEER technique (9) adapted for SNARF-1 (10). This technique requires the simultaneous acquisition of 2 confocal images that are produced by alternating line by line (line interweaving) of 2 excitation wavelengths (543 nm and 594 nm) and 2 emission ranges (550 -604 nm and 620 -715 nm).…”

“…When phagocytosis was studied, the responses of many cells were averaged (5,8). A powerful new imaging approach, confocal microscopy using the fluorescent pH indicator SNARF-1 enhanced by shifted excitation and emission ratioing (SEER) (9,10) enabled us to examine the responses of individual cells with high spatial and temporal resolution. We report here that the behavior of individual human neutrophils during phagocytosis differs markedly from the prevailing view.…”

Drug-Induced Anaphylaxis

“…Although these have been proposed for subjects with NSAID hypersensitivity caused by cross-intolerance [83], they show a high number of false positives [84,85]. However, the basophil activation has proved to be useful for beta-lactam [86], selective reactions to pyrazolones [81,85], omeprazole [87], ranitidine [88], and other agents [89].…”

On the role of water density fluctuations in the inhibition of a proton channel

“…Hv1 plays major roles in controlling B-cell proliferation, human sperm motility, and acid extrusion in lung epithelial cells (4,5), and it is involved in immunological processes, such as phagocytosis (1,6) and histamine secretion (7). Unlike other voltage-gated ion channels (VGICs), Hv1 is composed of two identical transmembrane (TM) subunits.…”