RESUMEN
The effect of vesicles of purified egg yolk phosphatidylcholine on the fertilizing capacity and acrosome breakdown of amphibian spermatozoa was studied. When Bufo arenarum spermatozoa were incubated with either small unilamellar vesicles (prepared by sonication) or with large unilamellar vesicles (prepared by reverse-phase evaporation) a decrease in the fertilizing capacity of spermatozoa was found. At the same phosphatidylcholine concentration, large unilamellar vesicles were more inhibitory than small unilamellar vesicles. The inhibition was dependent upon the phospholipid concentration and the length of the incubation period. Small unilamellar vesicles did not modify the time course of acrosome breakdown in Leptodactylus chaquensis, while large unilamellar vesicles markedly accelerated the rate of acrosome breakdown. In both biossays, the charge of the vesicles (made either positive or negative by the addition of 5% stearylamine or 5% phosphatidic acid) did not influence their biological effect. Multilamellar vesicles did not alter the fertilizing capacity nor the acrosome breakdown. We conclude that the size and the structure of the vesicles are important parameters in determining the inhibitory capacity of phosphatidyl choline on amphibian fertilization.
