High potassium concentration and the cumulus corona oocyte complex stimulate the fertilizing capacity of human spermatozoa

Progressively motile spermatozoa were incubated for 24hours in culture media containing 4.7 or 25mMK, in the presence or absence of hamster cumulus oophorus. The percentage of spermatozoa with progressive motility was significantly higher at 24hours in the presence of cumulus corona oocyte complexes, irrespective of K concentration. A significant decrease in sperm mortality was observed with the association of 25mMK and cumulus cells. A higher percentage of acrosome reaction was observed in spermatozoa incubated in 25mMK when compared with 4.7mMK, irrespective of time and the presence or absence of cumulus. The percentage of penetrated oocytes at 2 and 5hours of incubation was higher when sperm had been incubated in 25mMK than in 4.7mMK. The presence of cumulus in the culture medium induced an additional significant increase in the percentage of penetrated oocyte. Although at 24hours of incubation the percentage of acrosome reaction was higher than at 2 and 5hours, the percentage of penetrated oocytes did not increase proportionally.