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Sperm Need Calcium Kick to Succeed
By Cheryl Simon Silver

Hyperactivity has its place. In the last seconds before fertilization, a sperm, somehow spurred by a spike of intracellular calcium, launches into high gear. Without this final, frenzied burst of energy, the sperm cannot penetrate the egg’s outer layers and will never merge its DNA with that cloistered within the egg’s protective membrane.

Now scientists know why some sperm lack the necessary kick to finish the job: The calcium delivery channel known as CatSper2 is either blocked or not switched on.

The finding, published in the Proceedings of the National Academy of Sciences, suggests a new avenue for contraception. Down the road, a fast-acting cream containing a drug designed to block the calcium channel could remove the sperm from the reproductive race. Side effects would probably be few because the channel blocker would target a single protein in sperm cells.

A research team, led by David L. Garbers of the University of Texas Southwestern Medical Center in Dallas, zeroed in on the role of calcium in male infertility. Calcium levels within the sperm cells increase when it is time for “hyperactivation” and this spike may be the power surge that helps the sperm to penetrate an egg.

When the scientists cut off the calcium channel, the sperm lost the power to fertilize the egg. What’s more, when they disrupted the CatSper2 gene in male mice, the males became infertile, providing further evidence that in some cases this gene may contribute to infertility.

Team member Timothy Quill, also at University of Texas Southwestern Medical Center, says the research might lead to a new way to pinpoint a cause for some cases of infertility, but treatment is a more remote likelihood.

”We might be able to find some way to turn the calcium channel on, but we would also need to turn it on at the right time,” Quill says. “And we still don’t understand how the female regulates the timing of the process.”

Says Quill: “This is just one small piece. We’ve got a whole lot left to do.”

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Garbers, D. et al. Hyperactivated Sperm Motility Driven by CatSper2 Is Required for Fertilization. Proc Natl Acad Sci USA 100, 14869-14874 (December 9, 2003).


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