University of California, San Francisco, biologists Yuriy Kirichok and Polina Lishko have uncovered how progesterone -- a hormone involved in menstruation and embryo development -- switches on a sperm's internal electricity.
The electric current kicks sperm tails into overdrive, powering the final push toward the egg, the husband-and-wife researchers said.
Sperm that fail to respond to progesterone's signal could help explain why some couples have difficulty conceiving, Kirichok and Lishko, both Ukrainian immigrants, said.
The researchers have been using a technique called "whole-cell recording" to perform some of the world's first electrical recordings from human sperm to map out a key process in fertilization.
"For the first time, we have a reliable method to record, in a very direct fashion, the molecules that control male fertility," Kirichok told the San Jose Mercury News. "Now I believe the field will move faster."
And if progesterone molecules excite sperm tails, then blocking them with some drug that keeps progesterone from interacting with sperm could lead to an effective male birth control pill, researchers said.