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At least 19 recordsLinked to original sources

PubMed1976

Evidence for the role of a trypsin-like enzyme in the hamster sperm acrosome reaction.

Acrosome reactions occurring in vitro in hamster sperm capacitated by bovine follicular fluid were severly inhibited by four synthetic trypsin inhibitors and by Zn2+. Three polypeptide trypsin inhibitors and a synthetic chymotrypsin inhibitor did not inhibit the acrosome reaction, and Ca2+ overcame the inhibition by Zn2+. These results suggest that a trypsin-like enzyme (possibly acrosin) plays a role in the acrosome reaction.

Acrosin↗

PubMed1993

Role of diacylglycerols and calcium in the marsupial acrosome reaction.

Acrosomal loss was induced in marsupial spermatozoa by an intermediate of the phosphoinositide pathway. The diacylglycerol, 1,2-dioctanoyl-sn-glycerol (DiC8; 100 mumol l-1) induced acrosomal loss in 70% of brushtail possum (Trichosurus vulpecula) spermatozoa and in 80% of tammar wallaby (Macropus eugenii) spermatozoa. The DiC8-induced acrosomal loss was not enhanced by co-incubation with calcium ionophore A23187 and occurred in Ca(2+)-free medium and in the presence of the calcium chelator EGTA (3 mmol l-1). There was no evidence of uptake of 45Ca2+ during the DiC8-induced acrosomal loss. Inhibitors of protein kinase C [1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine] and phospholipase A2 [dexamethasone] did not effect DiC8-induced acrosomal loss in wallaby spermatozoa. The phorbol ester, phorbol 12-myristate 13-acetate, at a concentration of 10 mumol l-1 had no effect on possum spermatozoa and induced acrosomal loss in only 6% of wallaby spermatozoa. It appears that the DiC8-induced acrosome reaction is not mediated by activation of the phosphoinositide pathway and that extracellular calcium is not required for the membrane fusion event. As acrosomal loss was seen only at relatively high concentrations of diacylglycerol (> 50 mumol l-1) and there is no evidence of involvement of other phosphoinositide intermediates or analogues, it is likely that its role is as a direct membrane fusogen.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1996

A simple method for assessment of the human acrosome reaction of spermatozoa bound to the zona pellucida: lack of relationship with ionophore A23187-induced acrosome reaction.

Acrosome reactions induced by the calcium ionophore A23187 and zona pellucida (ZP) were studied. Sperm samples were obtained from fertile men or men with normal semen analysis and normal sperm-ZP binding. Oocytes were obtained, with the consent of the patients, after the failure of fertilization in vitro. Motile spermatozoa selected by a swim-up technique were incubated with 10 microM A23187 for 1 h, four oocytes for 2 h or solubilized ZP (4 ZP/microliters) for 2 h. Spermatozoa bound to the ZP were dislodged and collected in a small volume of phosphate-buffered saline by aspirating the oocytes with a glass pipette with an inner diameter (120 microns) slightly smaller than the diameter of the oocyte. The acrosome status of the spermatozoa was determined using fluorescein-labelled Pisum sativum agglutinin. The proportion of spermatozoa undergoing the acrosome reaction on the ZP at 2 h varied over a wide range (5-99%), but the agreement between results for the same semen sample exposed to different groups of oocytes was good: the standard deviations of the differences being 9%. Pre-incubation of spermatozoa for 2 h did not increase the ZP-induced acrosome reaction. Re-incubation of ZP with the same sperm suspension for 2 h after removing ZP-bound spermatozoa from the first 2 h incubation produced a significantly lower ZP-induced acrosome reaction in the second incubation (22 +/- 16%) than in the first incubation (30 +/- 14%; P < 0.001, n = 20). There was no significant difference in the ZP-induced acrosome reaction with oocytes with ZP which had or had not been penetrated by spermatozoa during the in-vitro fertilization insemination. Pre-incubation of spermatozoa with solubilized ZP blocked sperm-ZP binding. However, the acrosome reaction induced by solubilized ZP (4 ZP/microliters) was significantly lower than the acrosome reaction induced by intact ZP (10 +/- 5 and 30 +/- 13% respectively, n = 11, P < 0.001), but there was a high correlation (Spearman r = 0.822, P < 0.01) between the results. On the other hand, although the average of the acrosome reaction was similar for A23187 (42%) and for ZP (43%), there was no significant correlation between the results for the two stimuli (n = 60). In conclusion, a useful method for assessing the ZP-induced acrosome reaction has been developed using oocytes which failed to fertilize in vitro. The lack of a relationship between the result of the chemical (A23187) and physiological (ZP) stimuli for the acrosome reaction in the same subjects questions the biological basis of using A23187 for tests of sperm function. Solubilized human ZP in a concentration that blocks sperm-ZP binding is a less efficient inducer of the acrosome reaction than is intact ZP. It is possible that the three-dimensional structure of the ZP is important for induction of the acrosome reaction or that spermatozoa which bind to the ZP are more likely to acrosome react. Assessment of the physiological acrosome reaction for diagnosis of sperm defects which interfere with the fertilization process should be concentrated on the spermatozoa which are capable of binding to the ZP.

Acrosome↗

PubMed1992

A transient rise in intracellular Ca2+ is a precursor reaction to the zona pellucida-induced acrosome reaction in mouse sperm and is blocked by the induced acrosome reaction inhibitor 3-quinuclidinyl benzilate.

The acrosome reaction induced by the zona pellucida in mouse sperm has been shown to proceed in two stages experimentally distinguishable by the fluorescent probe chlortetracycline. Entry into the first stage of sperm bound to isolated, structurally intact zonae pellucidae is blocked by the compound 3-quinuclidinyl benzilate. In this study, we show, utilizing the fluorescent Ca2+ indicator fluo-3, that the first stage of the zona-induced acrosome reaction is characterized by an increase in intracellular Ca2+, followed by a decrease as the acrosome reaction proceeds. This calcium transient is completely suppressed by 3-quinuclidinyl benzilate. We conclude that the Ca2+ transient is induced by the zona pellucida and is required for the zona-induced acrosome reaction. Blockage of this sperm intracellular Ca2+ transient provides a mechanism for the inhibitory action of 3-quinuclidinyl benzilate on the zona-induced acrosome reaction in mouse sperm.

Acrosome↗

PubMed1992

The ionophore-induced acrosome reaction differs structurally from the spontaneous acrosome reaction.

The ultrastructure of the spontaneous acrosome reaction in ram spermatozoa has been compared with that induced by the ionophore, A23187. The spontaneous event was dependent on incubation for 4 h, on the temperature, and on dilution. Apart from the more rapid occurrence of the ionophore-induced event, the mean diameter and distribution of vesicle size was also different. The ionophore-induced vesicles were larger, more irregular, and heterogeneous in size compared with those occurring in the spontaneous acrosome reaction (average diameter 84 nm vs. 60 nm in the spontaneous acrosome reaction). These observations are interpreted in relation to capacitation.

Acrosome↗

PubMedDate not supplied

Effect of phorbol diesters, synthetic diacylglycerols, and a protein kinase C inhibitor on the human sperm acrosome reaction.

The acrosome reaction of spermatozoa may be analogous to various somatic cell exocytotic events that incorporate cascade reactions. One such cascade system involves the hydrolysis of a membrane-bound phospholipid; generation of the intracellular second messenger, diacylglycerol; and activation of protein kinase C, followed by the phosphorylation of a number of intracellular proteins. Stimulators of protein kinase C, phorbol diesters and synthetic diacylglycerols, were evaluated to determine if this system functions in the human sperm acrosome reaction. Phorbol 12-myristate 13-acetate and 4 beta-phorbol 12,13-didecanoate caused a significant (P less than 0.01) increase in the acrosome reaction of capacitated spermatozoa. Conversely, an inactive phorbol diester had no significant (P greater than 0.05) stimulatory effect on the acrosome reaction. The synthetic diacylglycerols, 1-oleoyl-2-acetyl-sn-glycerol, 1,2-dioctanoyl-sn-glycerol, and 1,2-dioleoyl-sn-glycerol caused a significant (P less than 0.01) increase in the acrosome reaction of capacitated spermatozoa, and to a similar extent as the phorbol diesters. A nonactivating isomer of 1,2-dioleoyl-sn-glycerol, 1,3-diolein, had no significant (P greater than 0.05) stimulatory effect on the acrosome reaction. Protein kinase C activation is a diacylglycerol-dependent and Ca2(+)-dependent process, and stimulation of the acrosome reaction by 1,2-dioctanoyl-sn-glycerol required the presence of calcium ions in the capacitation medium. An inhibitor of protein kinase C, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), prevented the diacylglycerol-induced acrosome reaction (P less than 0.01). These results support the hypothesis that protein kinase C, via activation by the intracellular second messenger diacylglycerol, has a role in the human sperm acrosome reaction.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1993

[The characteristics of monoclonal antibodies and their antigens associated with human sperm acrosome reaction. I. The induction of acrosome reaction and monoclonal antibody production].

Sperm released from the male genital tract must undergo capacitation and acrosome reaction (AR) before binding to oocyte membrane. Changes of sperm components have been found after the capacitation and AR. Based on these changes, the new contraceptive methods and the treatment of the male infertility might be approached. In the present study, in vitro capacitated human sperm were induced to undergo AR in BWW-BSA medium with calcium ionophore A 23187. The fresh human AR sperm in about 50% of sperm population assayed by triple stain technique and/or chlortetracycline fluorescence staining were used for immunization. Twenty three murine hybridomas secreting monoclonal antibodies (McAbs) to non-treated (NT) and/or AR human sperm have been obtained. Of them, 21 McAbs were classified as IgM, others as IgG1 and IgG2a. Based on the immunoreactions of 23 McAbs with NT and AR sperm, they were divided into three groups: group A reacted mainly with the AR sperm, group B with NT sperm, and group C with both AR and NT sperm. The cross reaction of these McAbs with human leukemia cell lines was detected by ELISA and the discrepant reactions were observed.

Acrosome↗

PubMed1985

[The influence of various molecules on the occurrence of the human sperm acrosome reaction].

The acrosome reaction is essential for fertilization, but the mechanism of the acrosome reaction of human spermatozoa is not clear at the present time. We studied the mechanism to analyze the cause of unexplained infertility, the appropriate timing of insemination, and the environment of spermatozoa prior to fertilization. For this study, we examined the effects of Ca++, Mg++, Kallikrein, Phospholipase A2, p-bromophenacyl bromide (Phospholipase A2 specific inhibitor), Lysophosphatidyl choline, Arachidonic acid, and Glyceryl monooleate using in vitro penetration assay employing zona- free hamster eggs. Results obtained were as follows. When human spermatozoa were incubated in mBWW with Ca++ or (and) Mg++ free medium, the acrosome reaction was inhibited. When human spermatozoa were incubated in mBWW with Kallikrein (1.0-4.0 KU ml), the acrosome reaction was promoted. When Phospholipase A2 was used at concentrations of 0.2 and 2.0 unit/ml, penetration rates showed the same tendency as in the control. But when p-bromophenacyl bromide was tested at concentrations of 1 X 10(-5) - 1 X 10(-3)M, penetration rates were inhibited when compared with the control. When human spermatozoa were incubated in medium containing Lysophosphatidyl choline (50 micrograms/ml), Arachidonic acid (5-50 micrograms/ml), and Glyceryl monoleate (300-400 micrograms/ml), the acrosome reaction was accelerated.

Acrosome↗

PubMedDate not supplied

Identification of human HAPRIN potentially involved in the acrosome reaction.

The acrosome reaction in sperm is an exocytotic event required for fertilization. Previously, we isolated a novel haploid-germ-cell-specific gene in the mouse; this gene, named haprin, encodes the RING-finger, B-box-type zinc finger and coiled-coil domain (RBCC) motif protein and may be involved in the acrosome reaction. Here we report the molecular cloning and characterization of a human haprin ortholog. The deduced amino acid sequence of human haprin had 91% identity with the mouse ortholog. Transcripts of human haprin were detected exclusively in the testes. Western blot and immunocytochemical analyses detected HAPRIN protein in the testes and sperm. The protein was localized in the acrosomal region of sperm and disappeared after the acrosome reaction. Our results indicate that the function of HAPRIN is highly conserved in humans and mice and that the protein could play an important role in the regulation of the acrosome reaction.

Acrosome Reaction↗

PubMed2003

Haprin, a novel haploid germ cell-specific RING finger protein involved in the acrosome reaction.

The acrosome reaction (i.e. the exocytosis of the sperm vesicle) is a prerequisite for fertilization, but its molecular mechanism is largely unknown. We have identified a cDNA clone for a gene named haprin, which encodes a haploid germ cell-specific RING finger protein. This protein is a novel member of the RBCC (RING finger, B-box type zinc finger, and coiled-coil domain) motif family that has roles in several cellular processes, such as exocytosis. It is transcribed exclusively in testicular germ cells after meiotic division. Western blot and immunohistochemical analyses showed the molecular weight of Haprin protein to be Mr approximately 82,000. It was localized in the acrosomal region of elongated spermatids and mature sperm and was not present in acrosome-reacted sperm. The specific antibody against the RING finger domain of Haprin inhibited the acrosome reaction in permeabilized sperm. These results indicated that the novel RBCC protein Haprin plays a key role in the acrosome reaction and fertilization.

Acrosome↗

PubMedDate not supplied

Time course of spontaneous in vitro sperm acrosome reaction.

The acrosome reaction (AR) is an exocytotic process essential for sperm penetration of the zona pellucida and binding to the oocyte (DeJonge, 1994). Evaluation of in vitro AR can suggest fertility potential. The purpose of this study was to determine AR as a function of time after removal of sperm from the seminal fluid using a novel test, the Acrobeads test (Fertility Technologies, Natick, Massachusetts), which uses paramagnetic beads coated with MH61, a monoclonal antibody that binds to acrosome-reacted sperm. Specimens were acquired from known fertile donors (n = 9) and in vitro fertilization (IVF) patients (n = 8) with no apparent male factor on the day of the IVF and processed by a minipercoll wash at 30 minutes after ejaculation. An aliquot of washed sperm was then divided into two portions. The first was placed with the Acrobeads (according to the manufacturer's instructions) and assessed for bead binding after 6 and 24 hours with the beads. The second aliquot of washed sperm was held at room temperature for 24 hours, then exposed to the beads, with bead binding assessed at 6 and 24 hours later (30 and 48 hours after washing). The Acrobeads score was determined by assessing the binding of MH61 beads in each of four replicates with a resulting score of 1 (lowest) to 4 (highest). The mean (+/-SD) motility was 62.0% (7.5) at 6 hours, 52.3% (6.4) at 24 hours, 55.9% (10.4) at 30 hours, and 54.7% (8.4) at 48 hours after removal from the seminal fluid. At 6 hours after washing and exposure to the beads, the score was 0.077 (0.27) with a range of 0-1; one donor specimen gave a score of 1, while all others had a score of 0. At 24 hours postremoval from the semen, donor and patient sperm were positive for the test, with a mean score of 3.6 (0.65). The mean fertilization rate for the IVF patients was 64.4% (range 33-90). When sperm were held for 24 hours prior to the test, there was little or no bead binding 6 hours later (score of 0.46 +/- 0.77) and at 24 hours later (48 hours after washing) (mean score of 0.25 +/- 0.45). These data suggest that completion of the acrosome reaction occurs by 24 hours after removal of the sperm from the seminal fluid. Since the MH61 beads bind to specific residues on the inner acrosomal membrane, these data also suggest that following the acrosome reaction at 24 hours with removal of the outer acrosomal contents and acrosomal matrix, the inner acrosomal membrane may be modified in some way that does not allow MH61 beads to bind to the sperm.

Acrosome↗

PubMed1995

Human spermatozoa attach to trypsin-treated hamster zonae pellucidae but do not undergo acrosome reactions.

The acrosome reaction by spermatozoa is an indispensable prerequisite for fertilization, and zonae pellucidae of human oocytes induce this reaction in the human spermatozoa attached to them. Human spermatozoa can attach to the zona pellucida of hamster oocytes when the oocytes have been treated with trypsin. We examined whether or not trypsin-treated hamster zona pellucida induces the acrosome reaction of human spermatozoa. Ten semen samples from 7 donors of proven fertility were examined in the present study. Highly motile spermatozoa were obtained by a swim-up method, and pre-incubated for 1 or 6 hours in modified Biggers, Whitten and Whittingham's (mBWW) medium supplemented with human serum albumin. The spermatozoa were then co-incubated for 1 hour with trypsin-treated hamster oocytes to allow sperm attachment to the zona. The spermatozoa on the zona were incubated for 3 additional hours in the mBWW medium. The percentage of acrosome reacted spermatozoa (%AR) was determined before and after the 3-hours of incubation. The %AR in the sperm suspension was also determined. There was no significant difference in the %AR between the spermatozoa attached to the zona pellucida and those in suspension during the incubation for 3 hours. These results indicate that the trypsin-treated hamster zona pellucida does not induce the acrosome reaction of human spermatozoa.

Acrosome↗

PubMed1993

Induction of the acrosome reaction in human spermatozoa by human zona pellucida and effect of cervical mucus on zona-induced acrosome reaction.

OBJECTIVES: To investigate the induction of the acrosome reaction in human spermatozoa by the zona pellucida (ZP), cumulus oophorus, and cervical mucus (CM), and to examine the effect of cumulus oophorus and CM on the zona-induced acrosome reaction. DESIGN, PATIENTS, MAIN OUTCOME MEASURES: The acrosome status of spermatozoa from healthy donors that were cultured with salt-stored human ZP, cumulus oophorus, and/or cervical mucus was assessed using fluoresceinated pisum sativum agglutinin. RESULTS: The acrosome reaction rate after sperm attachment to the zona for 6 hours was 35.7% +/- 17.7%, which was higher than controls (2.8% +/- 1.9%). The acrosome reaction was not observed after passage through cumulus oophorus or CM; however, the acrosome reaction rate of spermatozoa passed through CM after the attachment to zona was 51.6% +/- 6.8%, a higher value in comparison with spermatozoa that had not passed through CM (25.6% +/- 9.4%). CONCLUSION: These data indicate that human ZP are capable of inducing the acrosome reaction in human spermatozoa; however, cumulus oophorus and CM are unable to do so. The data further provide evidence that CM promotes the zona-induced acrosome reaction in human spermatozoa.

Acrosome↗

PubMed1994

Progesterone-induced acrosome reaction: potential role for sperm acrosome antigen-1 in fertilization.

We have established a monoclonal antibody (mAb) AG7 defining a sperm acrosome antigen-1 (SAA-1) on spermatozoa from the human and several mammalian species. MAb AG7 inhibits fertilization of mouse eggs in vitro and in vivo. An important characteristic of mAb AG7 is its inhibition of the rise in intracellular calcium induced by progesterone in human spermatozoa. Here we show that, following the acrosome reaction, SAA-1 is lost from the cap of human spermatozoa but remains detectable in the equatorial region. Acrosome reaction assays demonstrated a clear difference between progesterone- and A23187-induced acrosome reactions. For induction of the acrosome reaction with progesterone, a minimum capacitation time of 6 h was required. A23187 induced the acrosome reaction regardless of capacitation time. MAb AG7 completely inhibited the progesterone-induced acrosome reaction, but not the A23187-induced acrosome reaction in human spermatozoa. Differences in the pattern of calcium flux induced by the two agents might account for this phenomenon. The inhibition of the progesterone-induced acrosome reaction by mAb AG7 implies a regulatory function of SAA-1 during the human sperm acrosome reaction.

Acrosome↗

PubMed1997

Effects of gamma-aminobutyric acid, progesterone and ionophore A23187 on acrosome reaction of tree shrew sperm in vitro: examination of acrosome reaction with an improved fluorescence microscopy.

A number of acrosome reaction (AR) initiators have been found to be effective in inducing AR of human, laboratory and domestic animal sperm. Using an improved simple fluorescence microscopy, effects of gamma-aminobutyric acid (GABA), progesterone and ionophore A23187 on sperm AR of tree shrew, a useful animal model in biomedical research, have been investigated. Spontaneous AR in 4.92-7.53% of viable sperm was observed. Complete AR in 10.31-18.25% of viable tree shrew sperm was obviously induced by 5 microM and 10 microM calcium ionophore A23187, 1 mM GABA, and 5 microM progesterone, and there were no significant differences between their abilities to initiate complete AR. No significant differences of AR percentages between 1- and 2-h treatments with A23187, progesterone and/or GABA were observed. These results suggested that the responses of tree shrew sperm to these AR initiators are similar to that of human and other mammalian sperm.

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PubMed2003

The role of F-actin cytoskeleton-associated gelsolin in the guinea pig capacitation and acrosome reaction.

The acrosomal reaction (AR) is a regulated sperm exocytotic process that involves fusion of the plasma membrane (PM) with the outer acrosomal membrane (OAM). Our group has described F-actin cytoskeletons associated to these membranes. It has been proposed that in regulated exocytosis, a cortical cytoskeleton acts as a barrier that obstructs membrane fusion, and must be disassembled for exocytosis to occur. Actin-severing proteins from the gelsolin family have been considered to break this barrier. The present study attempted to determine if gelsolin has a function in guinea pig sperm capacitation and AR. By indirect immunofluorescence (IIF), gelsolin was detected in the apical and postacrosomal regions of the head and in the flagellum in both capacitated and non-capacitated guinea pig spermatozoa. By Western blotting, gelsolin was detected in isolated PM and OAM of non-capacitated spermatozoa. Gelsolin and actin were detected in a mixture of PM-OAM obtained by sonication, and both proteins were absent in membranes of capacitated spermatozoa. Inhibition of three different pathways of PIP2 hydrolysis during capacitation did not cancel gelsolin loss from membranes. Gelsolin was detected by Western blotting associated to membrane cytoskeletons obtained after phalloidin F-actin stabilization and Triton-X treatment; additionally, by immunoprecipitation, it was shown that gelsolin is associated with actin. By electron microscopy we observed that skeletons disassemble during capacitation, but phalloidin prevents disassembly. A three-dimensional skeleton was observed that apparently joins PM with OAM. Exogenous gelsolin stimulates AR assayed in a permeabilized spermatozoa model. Results suggest that gelsolin disassembles F-actin cytoskeletons during capacitation, promoting AR.

Acrosome↗

PubMed2004

alpha-SNAP and NSF are required in a priming step during the human sperm acrosome reaction.

The acrosome is a membrane-limited granule that overlies the nucleus of the mature spermatozoon. In response to physiological or pharmacological stimuli it undergoes a special type of Ca2+-dependent exocytosis termed the acrosome reaction (AR), which is an absolute prerequisite for fertilization. Aided by a streptolysin-O permeabilization protocol developed in our laboratory, we have previously demonstrated requirements for Rab3A, N-ethylmaleimide-sensitive factor (NSF), several soluble NSF-attachment protein receptor (SNARE) proteins, and synaptotagmin VI in the human sperm AR. Here, we show that alpha-soluble NSF-attachment protein (alpha-SNAP), a protein essential for most fusion events through its interaction with NSF and the SNARE complex, exhibits a direct role in the AR. First, the presence of alpha-SNAP is demonstrated by the Western blot of human sperm protein extracts. Immunostaining experiments reveal an acrosomal localization for this protein. Second, the Ca2+ and Rab3A-triggered ARs are inhibited by anti-alpha-SNAP antibodies. Third, bacterially expressed alpha-SNAP abolishes exocytosis in a fashion that depends on its interaction with NSF. Fourth, we show a requirement for alpha-SNAP/NSF in a prefusion step early in the exocytotic pathway, after the tethering of the acrosome to the plasma membrane and before the efflux of intra-acrosomal Ca2+. These results suggest a key role for alpha-SNAP/NSF in the AR, and strengthen our understanding of the molecular players involved in the vesicle-to-plasma membrane fusion taking place during exocytosis.

Acrosome↗

PubMed2003

Scorpion toxins that block T-type Ca2+ channels in spermatogenic cells inhibit the sperm acrosome reaction.

The acrosome reaction (AR) is a Ca(2+)-dependent event required for sperm to fertilize the egg. The activation of T-type voltage-gated Ca(2+) channels plays a key role in the induction of this process. This report describes the actions of two toxins from the scorpion Parabuthus granulatus named kurtoxin-like I and II (KLI and KLII, respectively) on sperm Ca(2+) channels. Both toxins decrease T-type Ca(2+) channel activity in mouse spermatogenic cells and inhibit the AR in mature sperm. Saturating concentrations of the toxins inhibited at most approximately 70% of the whole-cell Ca(2+) current, suggesting the presence of a toxin-resistant component. In addition, both toxins inhibited approximately 60% of the AR, which is consistent with the participation of T-type Ca(2+) channels in the sperm AR.

Acrosome Reaction↗