Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10933791 | Developmental Biology | 2007 | 9 Pages |
Abstract
Human spermatozoa stimulated with progesterone (a product of the cumulus and thus encountered by sperm prior to fertilization in vivo) apparently mobilize Ca2+ and respond very differently according to the way in which the steroid is presented. A progesterone concentration ramp (0-3 μM) induces [Ca2+]i oscillations (repetitive store mobilization) which modify flagellar beating, whereas bolus application of micromolar progesterone causes a single large transient (causing acrosome reaction) which is apparently dependent upon Ca2+ influx. We have investigated Ca2+-mobilization and functional responses in human sperm exposed to 3 μM progesterone. The [Ca2+]i response to progesterone was abolished by 4 min incubation in 0 Ca2+ medium (2 mM EGTA) but in nominally Ca2+-free medium (no added Ca2+; 0 EGTA) a smaller, slow response occurred. Single cell imaging showed a similar effect of nominally Ca2+-free medium and â 5% of cells generated a small transient even in the presence of EGTA. When cells were exposed to EGTA-containing saline (5 min) and then returned to nominally Ca2+-free medium before stimulation, the [Ca2+]i transient was greatly delayed (â 50 s) and rise time was doubled in comparison to cells not subjected to EGTA pre-treatment. We conclude that mobilization of stored Ca2+ contributes a 'slow' component to the progesterone-induced [Ca2+]i transient and that incubation in EGTA-buffered saline is able rapidly to deplete this store. Analysis of flagellar activity induced by 3 μM progesterone showed an effect (modified beating) associated with the [Ca2+]i transient, in > 80% of cells bathed in nominally Ca2+-free medium. This was reduced greatly in cells subjected to 5 min EGTA pre-treatment. The store-mediated transient showed a pharmacological sensitivity similar to that of progesterone-induced [Ca2+]i oscillations (consistent with filling of the store by an SPCA) suggesting that the transient induced by micromolar progesterone is a 'single shot' activation of the same store that generates Ca2+ oscillations.
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Authors
K. Bedu-Addo, C.L.R. Barratt, J.C. Kirkman-Brown, S.J. Publicover,