Secret of Sperm-motility revealed!!

 

 image of sperm (from "google-images" )

The "Sperm" happens to be the ONLY naturally motile cell of the body. But, the exact mechanism of it's movement has always remained a mystery.

Yuriy Kirichok and his team from UCSD have identified the mechanism that triggers sperm's race to the egg, reports a study in Cell.

Rationale and hypothesis:

Not many people think about electricity when they talk about sperm cells and this is the first time someone actually recorded the cellular process in a human sperm. By measuring the electrical current passing through the sperm cell membrane, the researchers identified a channel that releases a flood of protons from a sperm cell, initiating its trip up the fallopian tubes and on to the egg.

While inside the testes, sperm remain immobile. But upon ejaculation, when sperm enter the vagina, their intracellular pH rises, prompting their initial movement from the vagina to the fallopian tubes.

Observations:

At rest, sperm cells are full of protons (acidified environment). Upon activation, the proton channel [voltage-sensor-only (Hv1) channel], pokes a hole in the sperm plasma membrane and the protons that have accumulated blow out (alkalinazation) and the sperm becomes activated.


Hv1 is confined to the principal piece of the sperm flagellum, where it is expressed at unusually high density. Robust flagellar Hv1-dependent proton conductance is activated by:
* membrane depolarization,
* an alkaline extracellular environment,
* endocannabinoid anandamide, naturally present in male and female reproductive tracts,
* and removal of extracellular zinc, a potent Hv1 blocker.

Methodology:

* used human sperm-cells.
* These guys have used the newly-improved, age-old technique of Patch-Clamp, to measure minute electrophysiological changes happening on the sperm-membrane during the different phases of it's motility.

Potential uses:

possibilities for male contraception and enhancing male fertility, which of course, as of now, seems to be a far cry. Even if it were feasible to develop a compound to block the Hv1 channel, the resulting contraceptive would likely be a unisex or female based contraception, not a male one since the entire physiological changes are driven by the female tract.

Snippet: Marijuana smokers may have fertility problems, Kirichok said, because the drug hyper-activates the
             channel and burns out the sperm prematurely. 

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Acid Extrusion from Human Spermatozoa Is Mediated by Flagellar Voltage-Gated Proton Channel

Polina V. Lishko, Inna L. Botchkina, Andriy Fedorenko, and Yuriy Kirichok.

Cell 140, 327–337, February 5, 2010.