R. Qiu et al., A HISTAMINE DERIVATIVE INCREASES INTRACELLULAR CALCIUM MOBILIZATION AND OXIDATIVE-METABOLISM IN HL-60 CELLS, Immunopharmacology, 26(3), 1993, pp. 213-224
Past work in our laboratory has shown that a derivative of histamine,
histamine-trifluoromethyl-toluidide (HTMT), has surprising tissue spec
ificity on lymphocytes and can produce remarkable immunosuppression. T
his study focuses on the effects of HTMT on Ca2+ mobilization and oxid
ative metabolism in undifferentiated and DMSO-differentiated HL-60 cel
ls. HTMT caused two phases of increases in intracellular calcium conce
ntrations ([Ca2+](i)) in HL-60 cells. The responses were dose dependen
t, with similar EC(50) values (1.7 x 10(-5)M for undifferentiated and
1.5 x 10(-5)M for differentiated cells). The increase in [Ca2+]i in di
fferentiated cells was much greater than in undifferentiated cells. Th
e maximum responses were observed after the undifferentiated cells wer
e incubated with DMSO for 7 days. The increase in [Ca2+](i) induced by
HTMT in both types of cells was competitively antagonized by high con
centrations of histamine but not by classic histamine receptor antagon
ists (H-1, H-2, or H-3). The inhibitory effects of histamine on [Ca2+]
(i) accumulation in differentiated cells were partially reversed by hi
stamine H-2 receptor antagonist ranitidine, whereas in undifferentiate
d cells, the effects of histamine on Ca2+ mobilization were not affect
ed by ranitidine. Other cAMP elevating agents did not inhibit increase
s in [Ca2+](i) in undifferentiated cells but did affect [Ca2+](i) in d
ifferentiated cells. The enhanced response in [Ca2+](i) mobilization a
fter differentiation of HL-60 cells appeared to be the result of an in
crease in the expression/function of receptors for HTMT. One interesti
ng feature of this regulation was the fact that cAMP per se did not re
gulate HTMT induced Ca2+ mobilization in undifferentiated cells but in
hibited the mobilization in differentiated cells. HTMT caused the gene
ration of reactive oxygen species in both undifferentiated and differe
ntiated HL-60 cells as measured by chemoluminescence and the levels of
generation correlated with the mobilization of [Ca2+](i). In addition
, the EC(50)s for the HTMT induced calcium mobilization and the genera
tion of reactive oxygen species were similar, as was the case for hist
amine induced inhibition (K-i) in both cell types. The data imply a se
cond messenger role for Ca2+ in HTMT induced neutrophil activation.