Importance of Ca2+, K+ and glucose in the medium for sperm penetration through the human zona pellucida

When salt-stored human oocytes were inseminated in the regular mBWW medium and examined 6 hr later, the zonae of almost all of the oocytes were penetrated by spermatozoa. In contrast, none of zonae were penetrated when the oocytes were inseminated in either Ca(2+)-free, K(+)-free or glucose-free medium. The failure of zona penetration by spermatozoa in Ca(2+)-free and K(+)-free media is likely to be due to the inhibition of the acrosome reaction. Spermatozoa were unable to exhibit hyperactivated motility in glucose-free medium, suggesting that the failure of zona penetration in this medium is due, at least in part, to the inhibition of hyperactivated motility of spermatozoa.