“Since the channel is only in sperm, it is likely that the compound would affect no other cells in the body,” says Garbers.

The compound, if discovered, could theoretically be taken either by a man or woman, or even after sex, to prevent fertilization.

Also, the testes themselves would be protected from the drug because of a blood barrier that keeps out most large molecules. The only other such blood barrier is found in the brain.

Clapham says that he has received about 30 calls from news sources since he published his paper last month.

“My underlying feeling is that sex sells,” he says. “But all cell biology is interesting to me. Sperm behavior is very complicated.”

“You can think of the sperm as a single-celled human brain. There are many common proteins between the testes and the brain,” he says.

This observation is not surprising to some, he joked.

“Many women say, ‘We knew that already,’” Clapham says.

—Staff writer Jonathan H. Esensten can be reached at esensten@fas.harvard.edu.