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Type: Journal article
Title: Analysis of the mechanism by which calcium negatively regulates the tyrosine phosphorylation cascade associated with sperm capacitation
Author: Baker, Mark A.
Hetherington, Louise
Ecroyd, Heath William
Roman, Shaun D.
Aitken, R. John
Citation: Journal of Cell Science, 2004; 117(2):221-222
Publisher: Company of Biologists Limited
Issue Date: 2004
ISSN: 0021-9533
School/Discipline: School of Chemistry and Physics : Chemistry
Statement of
Mark A. Baker, Louise Hetherington, Heath Ecroyd, Shaun D. Roman, and R. John Aitken
Abstract: The capacitation of mammalian spermatozoa involves the activation of a cAMP-mediated signal transduction pathway that drives tyrosine phosphorylation via mechanisms that are unique to this cell type. Controversy surrounds the impact of extracellular calcium on this process, with positive and negative effects being recorded in independent publications. We clearly demonstrate that the presence of calcium in the external medium decreases tyrosine phosphorylation in both human and mouse spermatozoa. Under these conditions, a rise in intracellular pH was recorded, however, this event was not responsible for the observed changes in phosphotyrosine expression. Rather, the impact of calcium on tyrosine phosphorylation in these cells was associated with an unexpected change in the intracellular availability of ATP. Thus, the ATP content of both human and mouse spermatozoa fell significantly when these cells were incubated in the presence of external calcium. Furthermore, the removal of glucose, or addition of 2-deoxyglucose, decreased ATP levels within human spermatozoon populations and induced a corresponding decline in phosphotyrosine expression. In contrast, the mitochondrial inhibitor rotenone had no effect on either ATP levels or tyrosine phosphorylation. Addition of the affinity-labeling probe 8-N3 ATP confirmed our prediction that spermatozoa have many calcium-dependent ATPases. Moreover, addition of the ATPase inhibitor thapsigargin, increased intracellular calcium levels, decreased ATP and suppressed tyrosine phosphorylation. Based on these findings, the present study indicates that extracellular calcium suppresses tyrosine phosphorylation by decreasing the availability of intracellular ATP, and not by activating tyrosine phosphatases or inhibiting tyrosine kinases as has been previously suggested.
Keywords: Human spermatozoa; Capacitation; Tyrosine phosphorylation; Calcium; ATP
Rights: © The Company of Biologists Ltd 2004
DOI: 10.1242/jcs.00842
Appears in Collections:Chemistry and Physics publications

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