According to researchers at University of California at San Francisco (UCSF), Hv1, a molecule that activates sperm to swim also regulates intracellular pH levels is the likely missing link to prevent pregnancy and control male infertility.
On February 5, Cell, a peer-reviewed scientific journal, published "Acid Extrusion from Human Spermatozoa Is Mediated by Flagellar Voltage-Gated Proton Channel," this breakthrough study, found new insight into how the male reproductive system functions.
Yuriy Kirichok, PhD, lead researcher for the study at UCSF Department of Physiology, also proposed that these findings explain how marijuana use causes male infertility. Essentially the cannabis raises the pH level in the semen, causing the sperm to swim but without the endurance to make it all the way to the egg.
Conversely caffeine appears to have the opposite effect. According to study from the University of Sao Paolo, Brazil published in 2005 in Sao Paolo Medical Journal, men who drank coffee daily had strong swimming sperm opposed to men that didn't drink coffee.
This new research opens the door to further study and promises innovative approaches to male fertility and perhaps vasectomies.
PDF of full study in Cell: http://download.cell.com/pdf/PIIS0092867409016808.pdf?intermediate=true
Full study in Sao Paolo Medical Journal: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-31802005000400002