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

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