Hydrocortisone inhibits antigen-induced rise in intracellular free calcium concentration and abolishes leukotriene C4 production in leukemic basophils.
Antigenic stimulation of rat basophilic leukemia cells (RBL-3H3) elevates intracellular free Ca2+ concentration ([Ca2+]i) and induces production of leukotriene C4 (LTC4). This model was used to examine the role of Ca2+ in LTC4 formation, and inhibition by hydrocortisone (HC). HC, at a physiological concentration (2 x 10(-7) M), selectively prevented the stimulatory effect of the antigen on LTC4 production whereas the response to calcium ionophore (A23187) remained unimpaired. The inhibition by HC was time-dependent: half maximal response was reached at 2 hour and maximal response at 3 hours. Addition of arachidonic acid (3 micrograms/ml) did not overcome the inhibitory action of HC. An elevated [Ca2+]i is known to be essential for the activation of both 5-lipoxygenase and phospholipase A2. The stimulatory effect of the antigen on LTC4 production was abolished when the cells were incubated in Ca2+-deficient medium. Likewise, calcium ionophore stimulation shows dependence on extracellular Ca2+. Half maximal stimulation by the antigen and calcium ionophore was observed at external Ca2+ concentration of 150 microM and 40 microM respectively. Treatment with HC largely prevented the antigen-induced rise in [Ca2+]i, measured by Quin 2. In addition, HC reduced by 70% the accumulation of 45Ca2+ induced by the antigen. Collectively, these results demonstrate for the first time that HC reduces antigen-induced elevation of [Ca2+]i, and this may be associated with the inhibitory action of HC on LTC4 formation. This property could be partly responsible for the antiallergic and antiinflammatory activities of HC.
Zor
U
U
Department of Hormone, Research, Weizmann Institute of Science, Rehovot, Israel.
Her
E
E
Talmon
J
J
Kohen
F
F
Harell
T
T
Moshonov
S
S
Rivnay
B
B
D000818:Animals; D000941:Antigens / Q000276:immunology*; D001491:Basophils / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D006854:Hydrocortisone / Q000494:pharmacology*; D007942:Leukemia, Experimental / Q000378:metabolism; D013189:SRS-A / Q000096:biosynthesis*; D013050:Spectrometry, Fluorescence; D014407:Tumor Cells, Cultured / Q000378:metabolism
D000941:Antigens; D013189:SRS-A; D002118:Calcium; D006854:Hydrocortisone