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Progesterone initiation of the human sperm acrosome reaction: the obligatory increase in intracellular calcium is independent of the chloride requirement
Authors:KO Turner  MA Garcia  S Meizel
Affiliation:Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, 95616-8643, USA.
Abstract:The progesterone-initiated human sperm acrosome reaction (AR) requires a rise in intracellular Ca2+ (Ca2+]i), extracellular Cl- and apparently increased Cl- flux through a unique steroid receptor/Cl- channel resembling but not identical to a GABA(A)/Cl- channel complex. The present study uses fura-2 loaded human sperm, GABA(A)/Cl- channel blockers (picrotoxin and pregnenolone sulfate) and Cl(-)-containing and Cl(-)-deficient media to determine whether the progesterone-mediated increase in Ca2+]i is dependent on the Cl- requirement. There was no significant difference between the progesterone-mediated increases of Ca2+]i obtained in Cl(-)-containing and Cl(-)-deficient media. Picrotoxin did not significantly inhibit the progesterone-mediated increase in Ca2+]i, and pregnenolone sulfate increased Ca2+]i to the same extent as progesterone. These results strongly suggest that the increase in Ca2+]i essential to the AR is independent of the AR Cl- requirement and could be explained by the existence of two different sperm plasma membrane progesterone receptors.
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