by Linda Geddes, NewScientist
The switch that transforms sperm into super-swimmers in the race towards the egg has been identified at last. The discovery could lead to drugs that boost male fertility and new forms of male contraceptives. It could also explain why zinc deficiency and smoking cannabis can impair male fertility.
Sperm are relatively immobile before ejaculation. But once they get inside the female reproductive tract, they start swimming and speed up as they near the egg.
Although we've known for a while that sperm are prompted to swim by a rise in their internal pH caused by protons flowing out of the cell, the mechanism that regulates swimming was unknown.
The switch that transforms sperm into super-swimmers in the race towards the egg has been identified at last. The discovery could lead to drugs that boost male fertility and new forms of male contraceptives. It could also explain why zinc deficiency and smoking cannabis can impair male fertility.
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| Giving sperm a boost as they near their target (Image: Dr. David M. Phillips/Getty) |
Sperm are relatively immobile before ejaculation. But once they get inside the female reproductive tract, they start swimming and speed up as they near the egg.
Although we've known for a while that sperm are prompted to swim by a rise in their internal pH caused by protons flowing out of the cell, the mechanism that regulates swimming was unknown.
Proton flow
To investigate, Yuriy Kirichok at the University of California in San Francisco and his colleagues probed human sperm cells with "patch clamping", normally used to study nerve cells. This enabled them to monitor the flow of protons across the membrane.
They found that the sperm's tail contained large numbers of proton channels called Hv1 channels that respond to changes in pH and zinc concentration outside the cell. When the channels open, protons stream out of the sperm cells, causing the pH inside the cell to rise and the sperm to swim.
To investigate, Yuriy Kirichok at the University of California in San Francisco and his colleagues probed human sperm cells with "patch clamping", normally used to study nerve cells. This enabled them to monitor the flow of protons across the membrane.
They found that the sperm's tail contained large numbers of proton channels called Hv1 channels that respond to changes in pH and zinc concentration outside the cell. When the channels open, protons stream out of the sperm cells, causing the pH inside the cell to rise and the sperm to swim.
Since the uterus has a higher pH than semen, this difference may trigger the sperm to start swimming inside the female reproductive tract. High concentrations of zinc, such as those found in the male reproductive tract and in seminal fluid will keep channels from opening prematurely until the sperm are ready to start swimming. And because the concentration of zinc drops sharply and pH rises as sperm reach the fallopian tubes, this may trigger an extra spurt of swimming power as they near the egg.
--more at NewScientist.com
--more at NewScientist.com
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