Effects of Ca-ATPase inhibitors on the intracellular calcium activity and motility of human spermatozoa

Synergistic effect of extracellular adenosine triphosphate and quercetin on post-thaw quality and fertilization potential of Lohi ram sperm

This study determined the individual and combined effects of extracellular adenosine triphosphate (ATP) and quercetin (QUE) on the quality of post-thawed sperm and the fertilization potential of Lohi rams. In experiment 1, semen samples from four Lohi rams were pooled and extended with different concentrations of ATP or QUE (control; no ATP or QUE, 1 or 2 mM ATP and 10 or 20 μM QUE). In experiment 2, pooled semen samples were extended with various combinations of ATP and QUE (control; no ATP and QUE, 1 mM ATP + 10 μM QUE, 1 mM ATP + 20 μM QUE, 2 mM ATP + 10 μM QUE and 2 mM ATP + 20 μM QUE). All samples in both experiments were cryopreserved and analyzed for post-thawed sperm quality. In experiment 3, the best combination of ATP and QUE from experiment 2 was to extend semen, which was then used for laparoscopic insemination in estrus-synchronized ewes (n = 83). The results of experiment 1 showed that 1 mM ATP and 20 μM QUE treatments resulted in higher total motility, progressive motility, viability, plasma membrane intactness (PMI), and motion kinetics (VCL, VSL, VAP, LIN, and STR) compared to other treatments (p < 0.05). In experiment 2, the 1 mM ATP +10 μM QUE-treated group exhibited significantly higher total and progressive motility, PMI, and motion kinetics (VSL, VCL, VAP, STR, and BCF) compared to the control group (p < 0.05). In experiment 3, the fertilizing potential of sperms treated with 1 mM ATP +10 μM QUE was greater than that of untreated controls (58.1% vs. 27.5%, respectively, p-value = 0.012). In conclusion, the quality of post-thawed ram semen is enhanced when the extender is supplemented with extracellular 1 mM ATP and 20 μM QUE, whether used separately or in combination with 1 mM ATP and 10 μM QUE. Furthermore, the inclusion of 1 mM ATP and 10 μM QUE together in the extender significantly improves in vivo fertility in Lohi ram.

G protein-coupled estrogen receptor promotes acrosome reaction via regulation of Ca2+ signaling in mouse sperm

G protein-coupled estrogen receptor (GPER), a seven-transmembrane G protein-coupled receptor, mediates the rapid pre-genomic signaling actions of estrogen and derivatives thereof. The expression of GPER is extensive in mammal male reproductive system. However, the functional role of GPER in mouse sperm has not yet been well recognized. This study revealed that GPER was expressed at the acrosome and the mid-flagellum of the mouse sperm. The endogenous GPER ligand 17β-estradiol and the selective GPER agonist G1 increased intracellular Ca2+ concentration ([Ca2+]i) in mouse sperm, which could be abolished by G15, an antagonist of GPER. In addition, the G1-stimulated Ca2+ response was attenuated by interference with the phospholipase C (PLC) signaling pathways or by blocking the cation sperm channel (CatSper). Chlortetracycline staining assay showed that the activation of GPER increased the incidence of acrosome-reacted sperm. Conclusively, GPER was located at the acrosome and mid-flagellum of the mouse sperm. Activation of GPER triggered the elevation of [Ca2+]i through PLC-dependent Ca2+ mobilization and CatSper-mediated Ca2+ influx, which promoted the acrosome reaction in mouse sperm.

A genetically targeted sensor reveals spatial and temporal dynamics of acrosomal calcium and sperm acrosome exocytosis

Secretion of the acrosome, a single vesicle located rostrally in the head of a mammalian sperm, through a process known as "acrosome exocytosis" (AE), is essential for fertilization. However, the mechanisms leading to and regulating this complex process are controversial. In particular, poor understanding of Ca2+ dynamics between sperm subcellular compartments and regulation of membrane fusion mechanisms have led to competing models of AE. Here, we developed a transgenic mouse expressing an Acrosome-targeted Sensor for Exocytosis (AcroSensE) to investigate the spatial and temporal Ca2+ dynamics in AE in live sperm. AcroSensE combines a genetically encoded Ca2+ indicator (GCaMP) fused with an mCherry indicator to spatiotemporally resolve acrosomal Ca2+ rise (ACR) and membrane fusion events, enabling real-time study of AE. We found that ACR is dependent on extracellular Ca2+ and that ACR precedes AE. In addition, we show that there are intermediate steps in ACR and that AE correlates better with the ACR rate rather than absolute Ca2+ amount. Finally, we demonstrate that ACR and membrane fusion progression kinetics and spatial patterns differ with different stimuli and that sites of initiation of ACR and sites of membrane fusion do not always correspond. These findings support a model involving functionally redundant pathways that enable a highly regulated, multistep AE in heterogeneous sperm populations, unlike the previously proposed "acrosome reaction" model.

The Role of Selected Natural Biomolecules in Sperm Production and Functionality

Emerging evidence from in vivo as well as in vitro studies indicates that natural biomolecules may play important roles in the prevention or management of a wide array of chronic diseases. Furthermore, the use of natural compounds in the treatment of male sub- or infertility has been proposed as a potential alternative to conventional therapeutic options. As such, we aimed to evaluate the effects of selected natural biomolecules on the sperm production, structural integrity, and functional activity. At the same time, we reviewed their possible beneficial or adverse effects on male reproductive health. Using relevant keywords, a literature search was performed to collect currently available information regarding molecular mechanisms by which selected natural biomolecules exhibit their biological effects in the context of male reproductive dysfunction. Evidence gathered from clinical trials, in vitro experiments and in vivo studies suggest that the selected natural compounds affect key targets related to sperm mitochondrial metabolism and motion behavior, oxidative stress, inflammation, DNA integrity and cell death. The majority of reports emphasize on ameliorative, stimulating and protective effects of natural biomolecules on the sperm function. Nevertheless, possible adverse and toxic behavior of natural compounds has been indicated as well, pointing out to a possible dose-dependent impact of natural biomolecules on the sperm survival and functionality. As such, further research leading to a deeper understanding of the beneficial or adverse roles of natural compounds is necessary before these can be employed for the management of male reproductive dysfunction.

Long-term segmentation-free assessment of head-flagellum movement and intracellular calcium in swimming human sperm

Human spermatozoa are the archetype of long-term self-organizing transport in nature and are critical for reproductive success. They utilize coordinated head and flagellar movements to swim long distances within the female reproductive tract in order to find and fertilize the egg. However, to date, long-term analysis of the sperm head-flagellar movements, or indeed those of other flagellated microorganisms, remains elusive due to limitations in microscopy and flagellar-tracking techniques. Here, we present a novel methodology based on local orientation and isotropy of bio-images to obtain long-term kinematic and physiological parameters of individual free-swimming spermatozoa without requiring image segmentation (thresholding). This computer-assisted segmentation-free method evaluates, for the first time, characteristics of the head movement and flagellar beating for up to 9.2 min. We demonstrate its powerful use by showing how releasing Ca²⁺ from internal stores significantly alters long-term sperm behavior. The method allows for straightforward generalization to other bio-imaging applications, such as studies of bull sperm and Trypanosoma, or indeed of other flagellated microorganisms - appealing to communities other than those investigating sperm biology.

Effect of Quercetin Supplementation in Extender on Sperm Kinematics, Extracellular Enzymes Release, and Oxidative Stress of Egyptian Buffalo Bulls Frozen-Thawed Semen

Buffalo spermatozoa are more sensitive for cryopreservation compared to other species. This study aimed to evaluate the consequences of quercetin against cryodamage of buffalo frozen–thawed spermatozoa characteristics. Semen of Egyptian bulls (n = 4) was extended in OptiXcell extender incorporated with quercetin at 0 (control), 2.5, 5.0, 10.0, 20.0, 40.0, and 80.0 μM before cryopreservation. Frozen–thawed semen was evaluated for sperm motility by computer-assisted sperm analyzer (CASA), viability, morphology, membrane, and acrosome integrities. The kinematics parameters including average path velocity (VAP; μm/s), straight linear velocity (VSL; μm/s), curvilinear velocity (VCL; μm/s), amplitude of lateral head displacement (ALH; μm), beat cross frequency (BCF; Hz), linearity [LIN, (VSL/VCL) × 100], and straightness [STR, (VSL/VAP) × 100] were assessed. The sperm-free extender was evaluated for aspartate aminotransferase (AST), alanine aminotransferase (ALT), and H₂O₂. Homogenized sperm cells were evaluated for oxidative stress biomarkers [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX)], and lipid peroxidation [malondialdehyde (MDA)]. The highest values of total motility, progressive motility, viability, intact acrosome, and membrane integrity substantially improved with 10 μM of quercetin. STR (%) was substantially low (P < 0.01), and VCL (μm/s) and ALH (μm) were markedly high (P < 0.05) in 10 μM of quercetin. The outflow of ALT enzyme to extracellular fluid was lower with 10 μM of quercetin (P < 0.001) and higher at 2.5 μM of quercetin. The spermatozoa leaked AST was markedly lower at 5.0, 10 (P < 0.001) and 20 μM (P < 0.05) of quercetin. The activity of antioxidant enzymes was eminently low at all quercetin concentrations, and this was accompanied by the decrease in H₂O₂ in the media. SOD activity at 10–80 μM, CAT at 5.0–40 μM, and GPX at 2.5–80.0 μM of quercetin in spermatozoa were substantially low. MDA level significantly (P < 0.001) decreased at all quercetin concentrations. In conclusion, the incorporation of quercetin at the level of 10 μM is promising in improving buffalo semen characteristics and lower the freezing–thawing oxidative stress.

What happens to the unsuccessful spermatozoa?

To study apoptosis as a functional pathway in mature spermatozoa and apoptosis correlated to the acrosome reaction via the intracellular calcium concentration, semen samples from 27 healthy human donors were treated with inducers of apoptosis (betulinic acid, thapsigargin), inducers of the acrosome reaction (thapsigargin, calcium ionophore) or hydrogen peroxide to produce reactive oxygen species with and without prior incubation with a calcium chelator. Computer-assisted sperm analysis, flow cytometry, and transmission electron microscopy were performed to analyze changes in the acrosomal status and in apoptotic features. Betulinic acid, thapsigargin, and the calcium ionophore treatment resulted in an increased number of sperm cells with caspase 9 and caspase 3 activation, disrupted mitochondrial membrane potential, and a reacted acrosome. Sperm motility was decreased in all cases. Transmission electron analyses showed ultra-morphological changes, such as membrane integrity, membrane blebbing, the formation of head vacuoles, defects of the nuclear envelope, nuclear fragmentation, and the acrosome reaction. Acrosome reaction and apoptotic features decreased due to the reduction in intracellular calcium by the calcium chelator NP-EGTA, AM. Therefore, apoptotic cell death in acrosome-reacted sperm cells mediated by high intracellular calcium levels is possible.

Effect of Quercetin-loaded liposomes on induced oxidative stress in human spermatozoa

A strategy to circumvent the poor polyphenols bioavailability is to load these compounds into liposomes. We evaluated the in vitro effects of quercetin (Q) and Q-loaded liposomes (QLL, 30, 50, 100μM) on motility, viability and chromatin integrity of swim-up selected human sperm. Antioxidant power was assayed against tert-butylhydroperoxide induced lipid peroxidation (LPO) using C11-BODIPY581/591 fluorescent probe and transmission electron microscopy. QLL showed decreased toxicity for sperm motility and viability and increased DNA damage compared to Q. The percentage of sperm with fluorescence, marker of LPO, was decreased in samples incubated with Q vs QLL (P<0.001). The ultrastructure of acrosomes and membranes was preserved with Q 30/100μM, whereas QLL did not prevent membrane injury. Q alone appeared more effective than Q incorporated into liposomes; however liposomes could be considered as carriers that may convey different compounds inside sperm; they may therefore represent a field of research rich of many applications.

Plasma membrane Ca2+-ATPase 4: interaction with constitutive nitric oxide synthases in human sperm and prostasomes which carry Ca2+/CaM-dependent serine kinase

Deletion of the gene encoding the widely conserved plasma membrane calcium ATPase 4 (PMCA4), a major Ca(2+) efflux pump, leads to loss of sperm motility and male infertility in mice. PMCA4's partners in sperm and how its absence exerts its effect on fertility are unknown. We hypothesize that in sperm PMCA4 interacts with endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) which are rapidly activated by Ca(2+), and that these fertility-modulating proteins are present in prostasomes, which deliver them to sperm. We show that in human sperm PMCA4 is present on the acrosome, inner acrosomal membrane, posterior head, neck, midpiece and the proximal principal piece. PMCA4 localization showed inter- and intra-individual variation and was most abundant at the posterior head/neck junction, co-localizing with NOSs. Co-immunoprecipitations (Co-IP) revealed a close association of PMCA4 and the NOSs in Ca(2+) ionophore-treated sperm but much less so in uncapacitated untreated sperm. Fluorescence resonance energy transfer (FRET) showed a similar Ca(2+)-related association: PMCA4 and the NOSs are within 10 nm apart, and preferentially so in capacitated, compared with uncapacitated, sperm. FRET efficiencies varied, being significantly (P < 0.001) higher at high cytosolic Ca(2+) concentration ([Ca(2+)]c) in capacitated sperm than at low [Ca(2+)]c in uncapacitated sperm for the PMCA4-eNOS complex. These dynamic interactions were not seen for PMCA4-nNOS complexes, which had the highest FRET efficiencies. Further, along with Ca(2+)/CaM-dependent serine kinase (CASK), PMCA4 and the NOSs are present in the seminal plasma, specifically in prostasomes where Co-IP showed complexes similar to those in sperm. Finally, flow cytometry demonstrated that following co-incubation of sperm and seminal plasma, PMCA4 and the NOSs can be delivered in vitro to sperm via prostasomes. Our findings indicate that PMCA4 interacts simultaneously with the NOSs preferentially at high [Ca(2+)]c in sperm to down-regulate them, and thus prevent elevated levels of NO, known to induce asthenozoospermia via oxidative stress. Our studies point to the potential underlying cause of infertility in PMCA4's absence, and suggest that inactivating mutations of PMCA4 could lead to asthenozoospermia and human infertility. Screening for these mutations may serve both diagnostic and therapeutic purposes.

ATPases, ion exchangers and human sperm motility

Human sperm has several mechanisms to control its ionic milieu, such as the Na,K-ATPase (NKA), the Ca-ATPase of the plasma membrane (PMCA), the Na+/Ca2+-exchanger (NCX) and the Na+/H+-exchanger (NHE). On the other hand, the dynein-ATPase is the intracellular motor for sperm motility. In this work, we evaluated NKA, PMCA, NHE, NCX and dynein-ATPase activities in human sperm and investigated their correlation with sperm motility. Sperm motility was measured by Computer Assisted Semen Analysis. It was found that the NKA activity is inhibited by ouabain with twoKi(7.9×10−9and 9.8×10−5 M), which is consistent with the presence of two isoforms of α subunit of the NKA in the sperm plasma membranes (α1 and α4), being α4 more sensitive to ouabain. The decrease in NKA activity is associated with a reduction in sperm motility. In addition, sperm motility was evaluated in the presence of known inhibitors of NHE, PMCA and NCX, such as amiloride, eosin, and KB-R7943, respectively, as well as in the presence of nigericin after incubation with ouabain. Amiloride, eosin and KB-R7943 significantly reduced sperm motility. Nigericin reversed the effect of ouabain and amiloride on sperm motility. Dynein-ATPase activity was inhibited by acidic pH and micromolar concentrations of Ca2+. We explain our results in terms of inhibition of the dynein-ATPase in the presence of higher cytosolic H+and Ca2+, and therefore inhibition of sperm motility.

Mammalian sperm fertility related proteins

Infertility is an important aspect of human and animal reproduction and still presents with much etiological ambiguity. As fifty percent of infertility is related to the male partner, molecular investigations on sperm and seminal plasma can lead to new knowledge on male infertility. Several comparisons between fertile and infertile human and other species sperm proteome have shown the existence of potential fertility markers. These proteins have been categorized into energy related, structural and other functional proteins which play a major role in sperm motility, capacitation and sperm-oocyte binding. The data from these studies show the impact of sperm proteome studies on identifying different valuable markers for fertility screening. In this article, we review recent development in unraveling sperm fertility related proteins.

Stattic V, a STAT3 inhibitor, affects human spermatozoa through regulation of mitochondrial activity

We have recently shown that many mediators of the JAK/STAT signaling pathway are present in ejaculated human spermatozoa. Among them, STAT3 is detected mainly in membranes and flagellar cytoskeletal fractions. In order to determine the importance of STAT3-mediated signaling, sperm were incubated with Stattic V, a specific inhibitor. Effects on motility were evaluated by CASA, sperm acrosomal integrity was evaluated by FITC conjugated lectin (PSA or PNA) staining, and protein phosphotyrosine content was assessed by Western blot using a monoclonal anti-phosphotyrosine antibody. INDO1-AM and JC-1 were used to measure sperm intracellular calcium and mitochondrial membrane potential, respectively, by flow cytometry, and reactive oxygen species (ROS) production was investigated by luminol-based assay. Percentages of motility and motility parameters were significantly affected by Stattic V. This later also significantly increased intracellular Ca(2+) levels, progesterone- and calcium ionophore (A23187)-induced acrosome reaction. On the other hand, a significant decrease in ATP content was measured when sperm were treated with Stattic V, associated with depolarization of mitochondrial membrane and elevated ROS production. These results suggest that STAT3 is involved in sperm functions, at least through regulation of mitochondrial activity. This further emphasizes that STAT3 mediates cellular activities in a manner different than strictly the activation of gene transcription.

Effect of quercetin, rutin, naringenin and epicatechin on lipid peroxidation induced in human sperm

Quercetin, rutin, naringenin, epicatechin are flavonoids with diverse properties, including antioxidant potential. We evaluated, in vitro, the cytotoxicity of these flavonoids (20, 30, 50, 100, 200, 400 μM) in swim-up selected human sperm. Antioxidant activity was tested against tert-butylhydroperoxide induced lipid peroxidation using a C11-BODIPY(581/591) probe and transmission electron microscopy. A significant concentration-dependent effect on sperm viability (P<0.001) and motility (P<0.001) was observed. Lipid peroxidation was decreased in samples treated with 30 μM quercetin (P<0.01) and 30 μM rutin (P<0.05) versus samples incubated with tert-butylhydroperoxide alone. Naringenin (50-100 μM) showed a low protective effect and epicatechin (200 μM) was not efficacious. Transmission electron microscopy analysis confirmed the protective action of rutin and in particular quercetin on damages induced by lipid peroxidation. These results underlined the antioxidant properties of quercetin and rutin. A possible role of these compounds in the supplementation of media used during semen handling warrants attention and further studies.

Effect of ultraviolet C irradiation on human sperm motility and lipid peroxidation

PURPOSE

Ultraviolet C (UVC) irradiation of aqueous solutions is known to be a good source of reactive oxygen species (ROS). The aim of this study is to examine the effect of increasing doses of UVC irradiation, in the presence and absence of the antioxidant butylated hydroxytoluene (BHT), on human sperm motility and lipid peroxidation of its membranes.

MATERIALS AND METHODS

Human sperm samples were irradiated with UVC light (254 nm) for different periods of time. A computer-assisted semen analysis of sperm motility was carried out after UV irradiation. The percentage of motile sperm (%MOT), progressive motility, straight line velocity (VSL), curvilinear velocity (VCL) and the percentage of linearity (%LIN) were evaluated. The level of lipid peroxidation of sperm membranes was estimated by measurement of the thiobarbituric acid reactive substances (TBARS).

RESULTS

UVC irradiation of human spermatozoa produced a diminution of the sperm motility (%MOT, progressive motility, VSL, VCL, %LIN), viability and, concomitantly, an increase of the level of lipid peroxidation of the sperm membranes. The observed effects of the UVC irradiation were prevented by addition of the antioxidant BHT, indicating that the effects of UVC on the tested sperm parameters are mediated by an important rise in lipid peroxidation of the sperm membrane.

CONCLUSION

Lipid peroxidation of the human sperm plasma membrane leads to a decrease in the sperm motility (%MOT, progressive motility, VSL, VCL, %LIN) and viability. The protective effect of BHT on the UVC-irradiated sperm cells indicates the effects of ROS on sperm function.

Intrasperm Ca2+ modulation and human ejaculated sperm viability: influence of miconazole, clotrimazole and loperamide

Elevation of intrasperm Ca2+ is reported to influence viability of ejaculated spermatozoa. Human spermatozoa possess inositol triphosphate (IP3)-sensitive Ca2+ stores, which can be targeted for increasing intrasperm Ca2+ level. The influence of agents affecting Ca2+ homeostasis has been investigated. Miconazole nitrate, clotrimazole and loperamide hydrochloride produced a dose- and time-dependent decrease in viability, each requiring respectively 0.5, 1.0 and 1.0 mM for producing death of all sperm cells immediately upon addition to ejaculated human semen samples. The reduction in sperm viability was accompanied by elevation of intrasperm Ca2+ and was not affected by presence or absence of extracellular Ca2+. Significantly (P &lt; 0.05) less time was required for producing complete loss of sperm viability and increasing intrasperm Ca2+ when any of these drugs was added to sperm cells previously treated with selected agents affecting Ca2+ homeostasis. This enhanced spermicidal activity of miconazole, clotrimazole and loperamide appeared to be due to further mobilization of Ca2+ from partially depleted intrasperm Ca2+ stores. Synergism of spermicidal activity and intrasperm Ca2+ elevation by miconazole or clotrimazole was observed when Ca2+ efflux from sperm cells was simultaneously inhibited by 2′,4′-dichlorobenzamil hydrochloride, a Na+-Ca2+ exchange inhibitor. The spermicidal activity of miconazole, clotrimazole or loperamide due to elevation of intrasperm Ca2+ and its synergism, therefore, has great potential for exploitation of these drugs as contact spermicides.

Ca2+-stores in sperm: their identities and functions

Intracellular Ca2+ stores play a central role in the regulation of cellular [Ca2+](i) and the generation of complex [Ca2+] signals such as oscillations and waves. Ca2+ signalling is of particular significance in sperm cells, where it is a central regulator in many key activities (including capacitation, hyperactivation, chemotaxis and acrosome reaction) yet mature sperm lack endoplasmic reticulum and several other organelles that serve as Ca2+ stores in somatic cells. Here, we review i) the evidence for the expression in sperm of the molecular components (pumps and channels) which are functionally significant in the activity of Ca2+ stores of somatic cells and ii) the evidence for the existence of functional Ca2+ stores in sperm. This evidence supports the existence of at least two storage organelles in mammalian sperm, one in the acrosomal region and another in the region of the sperm neck and midpiece. We then go on to discuss the probable identity of these organelles and their discrete functions: regulation by the acrosome of its own secretion and regulation by membranous organelles at the sperm neck (and possibly by the mitochondria) of flagellar activity and hyperactivation. Finally, we consider the ability of the sperm discretely to control mobilisation of these stores and the functional interaction of stored Ca2+ at the sperm neck/midpiece with CatSper channels in the principal piece in regulation of the activities of mammalian sperm.

Characterization of a low-molecular-mass stimulator protein of Mg2+-independent Ca2+-ATPase: effect on phosphorylation/dephosphorylation, calcium transport and sperm-cell motility

A 14 kDa cytosolic protein purified from bovine brain homogenate has been recently reported as a stimulator of goat spermatozoa Mg2+-independent Ca2+-ATPase. In the present study, we demonstrate the formation of the [gamma-32P]ATP-labelled phosphoenzyme as the 110 kDa phosphoprotein and its rapid decomposition in presence of the stimulator protein. Together with the cross-reactivity of this 110 kDa protein with an anti-SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) 2a antibody, the ATPase can now be conclusively said to belong to the SERCA family, which is activated by the stimulator. The ability of the stimulator to enhance the Ca2+ transport has been elucidated from 45Ca2+ uptake studies and was found to be sensitive to Ca2+ channel blockers. CD revealed an alpha-helical structure of the stimulator. The amino acid analysis suggests that it is composed primarily of hydrophobic and some acidic amino acid residues. The pI of 5.1 has been re-confirmed from two-dimensional electrophoresis. Immuno-cross-reactivity studies indicate that the stimulator or similar proteins are present in cytosolic fractions of liver, kidney or testes in different species, but brain is the richest source. Proteomic analyses of its trypsinized fragments suggest its similarity with bovine THRP (thyroid hormone-responsive protein). The physiological significance of the stimulator has been suggested from its ability to activate sperm-cell motility.

Localization and regulation of plasma membrane Ca2+-ATPase in bovine spermatozoa

Calcium (Ca(2+)) signals, produced by the opening of plasma membrane entry channels, regulate a number of functions in spermatozoa such as capacitation and motility. The mechanisms of Ca(2+) removal from the sperm, required to restore resting [Ca(2+)](i), include plasma membrane Ca(2+)-dependent ATPase (PMCA) isoenzymes as well as a plasma membrane Na(+)-Ca(2+) exchanger. We have recently shown that bovine sperm PMCA is stimulated by PDC-109, a secretory protein of bovine seminal vesicles. To demonstrate the subcellular localization and regulation of bovine sperm PMCA, we have performed cell fractionation, enzyme activity determination and Western blotting studies of PMCA in spermatozoa removed from the cauda epididymidis of bull. Fractionation of sperm heads and tails resulted in a distinct association of ATPase activity with the tail membrane fraction. In vitro stimulation studies with PDC-109 using intact and fractionated sperm showed an increase in enzyme activity up to 105% in sperm tail membranes. Furthermore, thapsigargin inhibition did not alter the stimulatory effect of PDC-109 on ATPase activity, indicating that no sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA), but only PMCA isoenzymes are involved in this effect. Western blotting studies using a polyvalent PMCA antibody showed the exclusive presence of a 135 kDa band in the tail plasma membrane fraction. To elucidate whether or not the stimulatory effect was a direct one or indirectly mediated through PKA and PKC activation, PKA and PKC inhibitors, respectively, were used in the Ca(2+)-ATPase activity assays, which was followed by PDC-109 stimulation. The stimulatory effect of PDC-109 on PMCA was still observed under these conditions, while no phosphotyrosine proteins could be detected by Western blotting in sperm extracts following PDC-109 treatment. Co-immunoprecipitation studies, PDC-109 affinity chromatography as well as overlay blots failed to show a strong association of both PMCA and PDC-109, pointing to an indirect, perhaps phospholipid-mediated effect.

Stimulation of Mg2+-independent form of Ca2+-ATPase by a low molecular mass protein purified from goat testes cytosol

A low molecular mass protein purified from goat (Capra hircus) testes cytosol following gel filtration and anion exchange chromatographic separation stimulates Mg(2+)-independent Ca(2+)-ATPase activity without any significant effect on Mg(2+)-dependent Ca(2+)-ATPase. Stimulation of the ATPase is due to an increase in the rate of dephosphorylation of the overall reaction step of the enzyme. Binding of the stimulator increases the affinity of Ca(2+)-ATPase for Ca(2+). An analysis of enzyme kinetics reveals a reversible type of binding of the stimulator to the ATPase and non-competitive type of stimulation with respect to the substrate. Stimulation seems due to binding of the protein at a single site following Michaelis-Menten model. The protein can also counter the effect of calcium antagonists exerted on the ATPase. The pI of the protein is 6.2 and its molecular mass has been determined to be 13, 961 by Q-TOF-MS.

Calcium-induced quiescence of sperm motility in the bluegill (Lepomis macrochirus)

Before dilution in hypoosmotic media sperm of freshwater fish are maintained quiescent by a range of factors including osmolality, K+ and pH, and the onset of motility is generally associated with an increase in cytoplasmic Ca2+. In contrast, Ca2+ in conjunction with osmolality was found to inhibit motility of intact bluegill sperm. Consistent with seminal plasma composition, 0.16 mmol/L Ca2+ and greater, in conjunction with an osmotic concentration of 290 mOsm/kg, inhibited the onset of bluegill sperm motility; sperm diluted in saline at 290 mOsm/kg without Ca2+ became motile. Cations Mn2+ and Sr2+, in conjunction with osmolality, had an inhibitory effect on initiation of sperm motility similar to that of Ca2+. Sperm motility was inhibited by Ca2+ channel blockers nimodipine and nifedipine, the mitochondrial Ca2+ uniporter inhibitor ruthenium red and the calmodulin inhibitors W-7 and trifluoperazine dihydrochloride. These results provide evidence that elevated cytoplasmic Ca2+ inhibits sperm motility and yet low levels permit or promote motility. This study demonstrates a unique inhibitory action of Ca2+ on the motility of intact fish sperm at physiologically relevant levels.

Evidence for a secretory pathway Ca2+-ATPase in sea urchin spermatozoa

Plasma membrane, sarco-endoplasmic reticulum and secretory pathway Ca2+-ATPases (designated PMCA, SERCA and SPCA) regulate intracellular Ca2+ in animal cells. The presence of PMCA, and the absence of SERCA, in sea urchin sperm is known. By using inhibitors of Ca2+-ATPases, we now show the presence of SPCA and Ca2+ store in sea urchin sperm, which refills by SPCA-type pumps. Immunofluorescence shows SPCA localizes to the mitochondrion. Ca2+ measurements reveal that approximately 75% of Ca2+ extrusion is by Ca2+ ATPases and 25% by Na+ dependent Ca2+ exchanger/s. Bisphenol, a Ca2+ ATPase inhibitor, completely blocks the acrosome reaction, indicating the importance of Ca2+-ATPases in fertilization.

Calcium signalling in human spermatozoa: a specialized 'toolkit' of channels, transporters and stores

Ca(2+) is a ubiquitous intracellular messenger which encodes information by temporal and spatial patterns of concentration. In spermatozoa, several key functions, including acrosome reaction and motility, are regulated by cytoplasmic Ca(2+) concentration. Despite the very small size and apparent structural simplicity of spermatozoa, evidence is accumulating that they possess sophisticated mechanisms for regulation of cytoplasmic Ca(2+) concentration and generation of complex Ca(2+) signals. In this review, we consider the various components of the Ca(2+)-signalling 'toolkit' that have been characterized in somatic cells and summarize the evidence for their presence and activity in spermatozoa. In particular, data accumulated over the last few years show that spermatozoa possess one (and probably two) Ca(2+) stores as well as a range of plasma membrane pumps and channels. Selective regulation of the various components of the 'toolkit' by agonists probably allows spermatozoa to generate localized Ca(2+) signals despite their very small cytoplasmic volume, permitting the discrete and selective activation of cell functions.

Secretory pathway Ca2+-ATPase (SPCA1) Ca2+ pumps, not SERCAs, regulate complex [Ca2+]i signals in human spermatozoa

The sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitors thapsigargin (0.1-1 μM) and cyclopiazonic acid (10 μM), failed to affect resting [Ca2+] in human spermatozoa. Slow progesterone-induced [Ca2+ i]i oscillations in human spermatozoa, which involve cyclic emptying-refilling of an intracellular Ca2+ store were also insensitive to these inhibitors. Non-selective doses of thapsigargin (5-30 μM, 50-300 times the saturating dose for SERCA inhibition), caused elevation of resting [Ca2+]i and partial, dose-dependent disruption of oscillations. A 10-40 μM concentration of bis(2-hydroxy-3-tert-butyl-5-methyl-phenyl)methane (bis-phenol), which inhibits both thapsigargin-sensitive and -insensitive microsomal Ca2+ ATPases, caused elevation of resting [Ca2+]i and inhibition of [Ca2+]i oscillations at doses consistent with inhibition of thapsigargin-resistant, microsomal ATPase and liberation of stored Ca2+. Low doses of bis-phenol had marked effects on [Ca2+]i oscillation kinetics. Application of the drug to cells previously stimulated with progesterone had effects very similar to those observed when it was applied to unstimulated cells, suggesting that the sustained Ca2+ influx induced by progesterone is not mediated via mobilisation of Ca2+ stores. Western blotting for human sperm proteins showed expression of secretory pathway Ca2+ ATPase (SPCA1). Immunolocalisation studies revealed expression of SPCA1 in all cells in an area behind the nucleus, extending into the midpiece. Staining for SERCA, carried out in parallel, detected no expression with either technique. We conclude that: (1) intracellular Ca2+ store(s) and store-dependent [Ca2+]i oscillations in human spermatozoa rely primarily on a thapsigargin/cyclopiazonic acid-insensitive Ca2+ pump, which is not a SERCA as characterised in somatic cells; (2) effects of high-dose thapsigargin on spermatozoa primarily reflect non-specific actions on non-SERCAs and; (3) secretory pathway Ca2+ ATPases contribute at least part of this non-SERCA Ca2+ pump activity.

Stimulation of Human Spermatozoa with Progesterone Gradients to Simulate Approach to the Oocyte

Progesterone is present at micromolar concentrations in the cumulus matrix, which surrounds mammalian oocytes. Exposure of human spermatozoa to a concentration gradient of progesterone (0-3 microM) to simulate approach to the oocyte induced a slowly developing increase in [Ca(2+)](i) upon which, in many cells, slow oscillations were superimposed. [Ca(2+)](i) oscillations often started at very low progesterone (<10 nm), and their frequency did not change during the subsequent rise in concentration. Oscillations also occurred, but in a much smaller proportion of cells, in response to stepped application of progesterone (3 microM). When progesterone was removed, [Ca(2+)](i) oscillations often persisted or quickly resumed. Superfusion with low-Ca(2+) bathing medium (no added Ca(2+)) did not prevent [Ca(2+)](i) oscillations, but they could be abolished by addition of EGTA or La(3+). Inhibitors of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases or inositol trisphosphate signaling had no effect on [Ca(2+)](i) oscillations, but pharmacological manipulation of ryanodine receptors affected both their frequency and amplitude. Staining of live spermatozoa with BODIPY FL-X ryanodine showed localization of ryanodine binding primarily to the caudal part of the head and mid-piece. [Ca(2+)](i) oscillations did not induce acrosome reaction, but in cells generating oscillations, the flagellar beat mode alternated in synchrony with the oscillation cycle. Flagellar bending and lateral movement of the sperm head during [Ca(2+)](i) peaks were markedly increased compared with during [Ca(2+)](i) troughs. This alternating pattern of activity is likely to facilitate zona penetration. These observations show that progesterone initiates unusual and complex store-mediated [Ca(2+)](i) signaling in human spermatozoa and identify a previously unrecognized effect of progesterone in regulating sperm "behavior" during fertilization.