Evidence for the involvement of calmodulin in mouse sperm capacitation.
Although Ca(2+) is of fundamental importance in mammalian sperm capacitation, its downstream targets have not been definitively demonstrated. The purpose of this study was to use the calmodulin (CaM) antagonists W7 and calmidazolium (CZ) to investigate the possible role of CaM, a Ca(2+)-specific binding protein, in capacitation. Sperm membrane changes associated with capacitation were assessed by the B pattern after chlortetracycline staining and by the ability to undergo the acrosome reaction (AR) in response to lysophosphatidylcholine (LPC). The percentage of B pattern sperm was significantly inhibited by W7 or CZ in a concentration-dependent manner. At 100 microM W7 or 10 microM CZ, these inhibitors also significantly reduced the sperm's ability to undergo the LPC-induced AR. Inhibition of the B pattern and the LPC-induced AR was overcome by exogenous cAMP analogues. Treatment of the sperm with 100 microM W7 also resulted in a significant decrease in their ability to fertilize eggs in vitro. At 100 microM, W5, a less potent dechlorinated W7 analogue, had no effect on the B pattern, LPC-induced AR, or fertilization competence. Sperm viability and protein tyrosine phosphorylation were not substantially affected by 100 microM W7 (relative to 100 microM W5) or 10 microM CZ; however, the percentages of motile and hyperactivated sperm were significantly reduced. The antagonist-inhibited sperm motility was restored by dilution in control medium, but not by cAMP analogues. These results suggest that CaM participates in the regulation of membrane changes important for mouse sperm capacitation, at a point upstream from cAMP, and that this pathway is at least partially separable from pathways controlling tyrosine phosphorylation and hyperactivation.
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Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Olds-Clarke
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D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D020101:Acrosome Reaction / Q000187:drug effects; D000818:Animals; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005307:Fertilization in Vitro; D007093:Imidazoles / Q000494:pharmacology; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D011506:Proteins / Q000187:drug effects / Q000378:metabolism; D013075:Sperm Capacitation / Q000502:physiology*; D013081:Sperm Motility / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D002147:Calmodulin; D004791:Enzyme Inhibitors; D007093:Imidazoles; D008244:Lysophosphatidylcholines; D010726:Phosphodiesterase Inhibitors; D011506:Proteins; D013449:Sulfonamides; D013873:Thionucleotides; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016957:adenosine-3',5'-cyclic phosphorothioate; D014443:Tyrosine; C031938:calmidazolium; C017967:W 7; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine