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J. Biol. Chem., Vol. 263, Issue 2, 690-695, Jan, 1988
SE Domino and DL Garbers
The hydrolysis of phosphatidylinositol may generate multiple second
messengers, including inositol phosphates, 1,2-diacylglycerol, arachidonic
acid, and phosphatidic acid. Here, we describe for the first time in
spermatozoa that accumulation of one of these potential second messengers,
inositol 1,4,5-trisphosphate (1,4,5-IP3), can be stimulated by the
fucose-sulfate glycoconjugate (FSG) that induces an acrosome reaction. Sea
urchin spermatozoa were labeled with myo- [3H]inositol and incubated with
FSG. The amount of [3H]1,4,5-IP3 obtained from FSG-treated cells was up to
10 times that from untreated cells. Increases in the amount of
[3H]1,4,5-IP3 were detected within 30 s after addition of FSG (2.5-fold)
and were highest at 2 min after addition. Previously, it was shown that FSG
induces Ca2+-dependent increases in cyclic AMP concentrations (Kopf, G. S.,
and Garbers, D. L. (1980) Biol. Reprod. 22, 1118-1126). Increases in
[3H]1,4,5-IP3 accumulation caused by FSG were also dependent on
extracellular Ca2+. The Ca2+ channel blockers, verapamil and nifedipine,
inhibited increases in both [3H]1,4,5-IP3 and cyclic AMP, and the addition
of concentrations of extracellular Ca2+ higher than 9.6 mM could reduce the
inhibition. When spermatozoa were incubated in Ca2+-free seawater,
FSG-induced increases in [3H]1,4,5-IP3 and cyclic AMP concentrations were
blocked; addition of extracellular Ca2+ restored the responses. Other
treatments that result in the induction of an acrosome reaction, including
the addition of monovalent cation H+ exchangers, nigericin and gramicidin
S, and incubation in seawater at alkaline pH (pH 8.8), also stimulated
accumulation of [3H]1,4,5-IP3 and cyclic AMP.
The fucose-sulfate glycoconjugate that induces an acrosome reaction in spermatozoa stimulates inositol 1,4,5-trisphosphate accumulation
Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232.
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