Differential effect of hypertonicity on FMLP-, anti-IgE- and Ca2+ ionophore A23187-induced histamine release from human basophil leukocytes.

Effects of different extracellular Na+ and K+ concentrations (respectively, 135, 155, 220, 260 mM NaCl, and 2.7, 20, 50, 100 mM KCl) on IgE-dependent and IgE-independent histamine release from human basophils were examined. High extracellular Na+ and K+ concentrations were shown to reduce N-formyl-methionyl-leucyl-phenyl-alanine- (FMLP), but not anti-IgE- or Ca2+ ionophore A23187-induced histamine release. A high extracellular Ca2+ (7.2 mM CaCl2) concentration increased basophil response to anti-IgE and FMLP. The enhancement of FMLP- but not of anti-IgE-induced histamine release was antagonized by high extracellular Na+ and K+ concentrations. When leukocytes were suspended in isotonic choline chloride solutions (choline is a nonpermeant monovalent cation), an enhancement of anti-IgE- and FMLP-induced histamine release was observed. This suggests that monovalent cations, namely Na+ ions, at physiological concentrations, downregulate histamine release from human basophils. At high choline chloride concentrations, FMLP-, but not anti-IgE-induced histamine release was inhibited. Thus, the reduction of FMLP-evoked histamine secretion from human basophils seems to be due to hypertonicity and not to the type of monovalent cation, either permeant or nonpermeant, contained in extracellular milieu. The different effects of a hypertonic solution on anti-IgE and FMLP-induced histamine release are probably related to the different cell activation pathways triggered by the two stimuli.