An influx of extracelluar calcium is required for initiation of the human sperm acrosome reaction induced by human follicular fluid

Abstract

The role of Ca2+ in the human sperm acrosome reaction was investigated using the fluorescent calcium indicator fura-2. Previous experiments have shown that a Sephadex G-75 column fraction of human follicular fluid can stimulate the human sperm acrosome reaction [Suarez SS, Wolf DP, Meizel S (1986): Gamete Res 14:107-121]. Using fura-2, we demonstrated that this Sephadex G-75 fraction also stimulates a rapid, transient increase in intracellular free Ca2+. This Ca2+ transient is blocked either by chelation of extracellular calcium or by addition of the Ca2+ antagonist La3+. We have also been able to stimulate the acrosome reaction in human sperm without significant loss of motility, using the divalent cation ionophore ionomycin. Acrosome reactions stimulated by whole follicular fluid, the G-75 fraction, or ionomycin are all blocked by removal of extracellular Ca2+. These results strongly suggest that an influx of extracellular Ca2+ is responsible for initiating the acrosome reaction in human sperm treated with human follicular fluid. This is the first demonstration in mammalian sperm that a potentially physiological stimulus can cause an increase in intracellular Ca2+ concomitant with the acrosome reaction.

Forskolin stimulates porcine sperm capacitation by increasing calcium uptake

“…External Ca2' is an essential requirement for both processes [17] and the increases in Ca2+ influx during capacitation and at the initial step of the acrosome reaction were reported [3,4,16,18,19]. So, it is likely that agents which stimulate Ca2+ influx also promote both processes [20].…”

“…The increase in the intracellular Ca2' levels during capacitation and the concomitant acrosome reaction was directly measured with the fluorescent calcium indicator fura- [3,4], while the mechanism of Ca2' entry into the sperm remains unknown.…”

Influence of steroid hormone progesterone on the properties of phosphatidyl serine monolayers and thin liquid films

“…It is also proven in vitro that Prog could induce aggregation and fusion of membrane vesicles (the central event of acrosomal reaction) and this effect is strongly enhanced in presence of Ca 2+ [2,11].…”

“…Resent studies showed that progesterone [6], Ca2+ ions or cooperation of the two agents [8][9][10][11] could drive induction of acrosome reaction in vivo. It is also proven in vitro that Prog could induce aggregation and fusion of membrane vesicles (the central event of acrosomal reaction) and this effect is strongly enhanced in presence of Ca 2+ [2,11].…”

Influence of Progesterone and Gaba a Receptor on Calcium Mobilization During Human Sperm Acrosome Reaction

“…The AR is generally recognized as exposure of the inner acrosomal membrane over the anterior portion of sperm head in consequence of vesiculation between the plasma membrane and the outer acrosomal membrane [2,3]. The induction of AR needs a dramatic increase of cytosolic calcium in consequence of extracellular calcium influx [4,5]. In fact, AR can be induced spontaneously by incubation in an appropriate medium supplemented with calcium in vitro [6,7,8].…”