Fusion of sperm with prostasomes: effects on membrane fluidity.
Prostasomes are membranous vesicles (150-200 nm diameter) present in human semen. They are secreted by the prostate gland and contain large amounts of cholesterol, sphingomyelin, and Ca2+. In addition, some of their proteins are enzymes. Prostasomes enhance the motility of ejaculated sperm and are involved in a number of biological functions. In this work, we study the fusion of prostasomes to sperm by determining the relief of octadecylrhodamine self-quenching and the fluidity of membranes by measuring the fluorescence anisotropy of diphenylhexatriene. We present the following findings: (a) the contact of sperm cells with prostasomes at slightly acidic pH causes the fusion of the membranes; (b) the amount of transferred lipid depends on the prostasome/sperm ratio; (c) the fluidity of sperm is much higher than that of prostasomes; (d) the fusion changes some properties of sperm cells, such as fluidity, which decreases greatly; and (e) the extent of fluidity variations depends on the prostasome to sperm ratio. We propose that the H(+)-dependent fusion of prostasomes to sperm may have physiological consequences. In fact, this process can modify the lipid and protein pattern of sperm plasma membranes.
Carlini
E
E
Istituto di Biochimica e Chimica Medica, Perugia, Italy.
Palmerini
C A
CA
Cosmi
E V
EV
Arienti
G
G
D006801:Humans; D008297:Male; D008560:Membrane Fluidity; D008561:Membrane Fusion; D011467:Prostate / Q000378:metabolism*; D013094:Spermatozoa / Q000166:cytology*