Key molecule identified in driving chemo attraction between sperm and egg
When sperm capture chemoattractant molecules, the voltage becomes more negative, because potassium channels open and potassium ions leave the cell.
Over 100 years ago, researchers at the University of Chicago in the US discovered that eggs from marine invertebrates release a chemical factor that attracts sperm, a process called chemotaxis.
Sperm, for their part, swims up a chemical gradient to reach the egg, assisted by a pulsatile rise in calcium ion (Ca2+) concentration in the sperm tail that controls its beating, said researchers at Marine Biological Laboratory (MBL) in the US.
In the past years, many of the cellular components that translate chemoattractant stimulation into a Ca2+ response have been revealed, but a crucial ingredient has been missing, according to the study published in the journal Nature Communications.
A prerequisite for Ca2+ ions from the sperm's environment being able to enter the tail is that the sperm cell's pH becomes more alkaline.
The molecule that brings about this change in pH has been elusive.
Such so-called sodium/proton exchangers have been known for a long time, but this one is special, researchers said.
It is a chimaera that shares structural features with ion channels, called pacemaker channels, which control our heartbeat and electrical activity in the brain.
The voltage-sensor registers this voltage change and the exchanger begins exporting protons from the cell; the cell's interior becomes more alkaline, researchers said.
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