Progesterone initiation of the human sperm acrosome reaction: the obligatory increase in intracellular calcium is independent of the chloride requirement.
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.
Turner
K O
KO
Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, 95616-8643, USA.
Garcia
M A
MA
Meizel
S
S
D000177:Acrosome / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D011374:Progesterone / Q000494:pharmacology / Q000502:physiology*; D013084:Sperm-Ovum Interactions; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*
D002712:Chlorides; D011374:Progesterone; D002118:Calcium