Patterns of [Ca2+](i) mobilization and cell response in human spermatozoa exposed to progesterone

K Bedu-Addo, C L R Barratt, J C Kirkman-Brown, S J Publicover (Lead / Corresponding author)

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)

Abstract

Human spermatozoa stimulated with progesterone (a product of the cumulus and thus encountered by sperm prior to fertilization in vivo) apparently mobilize Ca(2+) and respond very differently according to the way in which the steroid is presented. A progesterone concentration ramp (0-3 microM) induces [Ca(2+)](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 Ca(2+) influx. We have investigated Ca(2+)-mobilization and functional responses in human sperm exposed to 3 muM progesterone. The [Ca(2+)](i) response to progesterone was abolished by 4 min incubation in 0 Ca(2+) medium (2 mM EGTA) but in nominally Ca(2+)-free medium (no added Ca(2+); 0 EGTA) a smaller, slow response occurred. Single cell imaging showed a similar effect of nominally Ca(2+)-free medium and approximately 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 Ca(2+)-free medium before stimulation, the [Ca(2+)](i) transient was greatly delayed (approximately 50 s) and rise time was doubled in comparison to cells not subjected to EGTA pre-treatment. We conclude that mobilization of stored Ca(2+) contributes a 'slow' component to the progesterone-induced [Ca(2+)](i) transient and that incubation in EGTA-buffered saline is able rapidly to deplete this store. Analysis of flagellar activity induced by 3 muM progesterone showed an effect (modified beating) associated with the [Ca(2+)](i) transient, in >80% of cells bathed in nominally Ca(2+)-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 [Ca(2+)](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 Ca(2+) oscillations.

Original languageEnglish
Pages (from-to)324-32
Number of pages9
JournalDevelopmental Biology
Volume302
Issue number1
DOIs
Publication statusPublished - 1 Feb 2007

Keywords

  • Acrosome/metabolism
  • Acrosome Reaction
  • Calcium/metabolism
  • Calcium Signaling
  • Chelating Agents/pharmacology
  • Egtazic Acid/pharmacology
  • Enzyme Inhibitors/pharmacology
  • Humans
  • Male
  • Progesterone/metabolism
  • Spermatozoa/cytology
  • Thapsigargin/pharmacology

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