FUSION OF HUMAN SPERM TO PROSTASOMES AT ACIDIC PH

Prostasomes are membranous vesicles (150-200 nm diameter) present in h uman semen. They are secreted by the prostate and contain large amount s of cholesterol, sphingomyelin and Ca2+. In addition, some of their p roteins are enzymes. Prostasomes enhance the motility of ejaculated sp ermatozoa and are involved in a number of additional biological functi ons. The possibility that they may fuse to sperm has never been proved . In this work, we studied the fusion of sperm to prostasomes by using various methods (relief of octadecyl Rhodamine B fluorescence self-qu enching, fluorescence microscopy and flow cytometry) and we found that it occurs at acidic pH (4-5), but not at pH 7.5. pH-dependent fusion relies on the integrity of one or more proteins and is different from the Ca2+-stimulated fusion between rat liver liposomes and spermatozoa that does not require any protein and occurs at neutral pH. We think that the H+-dependent fusion of prostasomes to sperm may have physiolo gical importance by modifying the lipid and protein pattern of sperm m embranes.