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J. Biol. Chem., Vol. 262, Issue 24, 11449-11454, 08, 1987
Calcium-independent phosphoinositide breakdown in rat basophilic leukemia cells. Evidence for an early rise in inositol 1,4,5- trisphosphate which precedes the rise in other inositol phosphates and in cytoplasmic calcium
VS Pribluda and H Metzger
Aggregation of the receptor with high affinity for immunoglobulin E (IgE)
in rat basophilic leukemia cells leads to a calcium-dependent and a
calcium-independent hydrolysis of phosphoinositides. The increase in the
levels of inositol phosphates induced in the absence of calcium is only 25%
of that observed with 1 mM Ca2+. The inositol phosphates reach a new steady
state level 2 min after stimulation in EGTA, whereas with calcium they
continue to increase up to 15 min. A similar response is observed when the
receptors are aggregated due to the interaction of bound IgE with antigen
or with anit-IgE, or by the binding of IgE cross- linked chemically. The
antigen-mediated response is inhibited by hapten and disruption of such
antigen-antibody aggregates late after stimulation leads to a rapid decline
in the levels of the inositol phosphates to basal values. Separation of the
inositol phosphates by Dowex columns shows that there is a fast rise in
inositol trisphosphate which peaks at 15 s and slowly declines to a lower
plateau within 2 min. Analysis by high pressure liquid chromatography
reveals a 5-fold increase in the levels of inositol 1,4,5-trisphosphate in
less than 10 s after stimulation, which precedes any major change in the
other inositol phosphates. Aggregation of the receptor in the absence of
external calcium induces a transient increase in cytoplasmic calcium which
reaches a maximum of approximately 25 nM over basal levels after
activation. The onset of the rise in Ca2+ lags after the initial rise in
the inositol 1,4,5-trisphosphate.

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Copyright © 1987 by the American Society for Biochemistry and Molecular Biology.
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