Perhaps you have seen it in the documentaries: the sperm cells appear to busy themselves in search of an ecstatic union with an ovum, flicking their tale or flagella with jet like propulsion.
Well, it ‘tis not so! The sperm’s mobility is short lived. When in the male reproductive tract they have to rest easy, lest they wear themselves out prematurely and give up any chance of ever finding an egg.
Scientists have long known that sperm’s activity level depends on their internal pH.
A channel that allows the tiny cells to rid themselves of protons and change their internal environment from acidic to alkaline has now been discovered reports the February 5th issue of the journal Cell.
Once the internal PH is altered the sperm cells their race to the finish line begins.
“The concentration of protons inside the [sperm] cell is 1,000 times higher than outside,” said Yuriy Kirichok of the University of California, San Francisco. “If you just open a pore, protons will go outside. We identify the molecule that lets them out.”
This discovery may lead to new ways of controlling male fertility, according to the researchers that include Polina V. Lishko, Inna L. Botchkina, Andriy Fedorenko, and Yuriy Kirichok.
Kirichok likens the quiescent sperm cells to balloons inflated with protons instead of air. If you open a hole in the sperm, protons will readily flow out.
Eeach sperm’s flagellum is covered in many Hv1 proton channels, that when activated by external cues, they open and protons escape from many pores at once.
There are many conditions that open up the Hv1 pore, said Kirichok, including alkaline conditions and the removal of zinc outside the cell.
They also open when exposed to the endocannabinoid known as anandamide, which is present in both the male and female reproductive tracts and may be at particularly high levels in the vicinity of the egg.
That raises an interesting possibility, Kirichok said.
Endocannabinoids are natural lipids that influence the activity of neurons. They act on the same receptors that the active component of marijuana.
This may explain why marijuana has been linked to impaired male fertility.
“Marijuana likely activates sperm prematurely, leaving them burnt out in a matter of hours,” said Kirichok.
The newly discovered Hv1 channel may allow for new ways to modify the activity of sperm in either direction, Kirichok said.
Many key biochemical reactions in sperm depend on intracellular pH levels, including its initial activation, hyperactivation once near the fallopian tubes and the acrosome reaction, in which enzymes are released to penetrate the egg.
“You can imagine now that we know the molecule responsible we could block it to prevent activation and fertilization as a kind of male contraception” he said.
On the other hand, you might also give some sperm the extra boost they need.
Source: Adapted from a Cell Press Press Release
