Regulation of human basophil activation. IV. Dissociation between cationic dye binding and histamine release: role of Ca²⁺ions*

This is the authors' abstract. We don't add key points for this paper.

In previous studies we observed that in vitro histamine release from human basophils could be dissociated from the loss of affinity of basophil granules for a cationic dye, toluidine blue. In the present study we further explored the intracellular signals leading to the decrease in toluidine blue positive basophil (TB+) numbers, with or without histamine release. Since Ca2+ mobilization is a crucial event in secretion and particularly in histamine release, we studied the role of Ca2+ in histamine release as compared to TB+ decrease. In the presence of external Ca2+ (2 mM): i) Ca2+ channel antagonists verapamil and nifedipine up to 10 microM were without effect on IgE-mediated histamine release and TB+ decrease; ii) loading of the leucocytes with Quin2 or preincubation with TMP-8, an internal Ca2+ antagonist, significantly inhibited the release of histamine and the decrease of TB+ basophils. In the absence of added external Ca2+:i) histamine release was abolished whereas the decrease of TB+ was not modified, even in the presence of EGTA;ii) the decrease of TB+ could be inhibited by prolonged EGTA preincubation, by Quin2 loading and incubation with TMB-8. We conclude that histamine release requires both external Ca2+ influx and mobilization of internal Ca2+. In contrast, no influx of external Ca2+ is required for TB+ decrease in which, however, internal Ca2+ mobilization appears to play an important role.