Rise of internal Ca2+ accompanies the initiation of trout sperm motility

Effects of temperature on sperm motility of burbot Lota lota: spontaneous activation and calcium dependency

Several factors regulating activation of spermatozoon motility in Eurasian burbot, Lota lota, including osmolality, calcium (Ca²⁺ ) ions, and temperature were investigated. Spermatozoon motility in Eurasian burbot, Lota lota was assessed at 4 and 30°C in seminal fluid, isotonic media (with and without Ca²⁺ ) and hypotonic media (with and without Ca²⁺ ). Spermatozoa were spontaneously activated in seminal fluid at 20°C and the maximum motility was recorded at 30°C, which is out of the spawning temperature range, indicating that no risk of activation occurs during routine semen handling in artificial insemination. Initiation of spermatozoon motility in L. lota is mediated by Ca²⁺ and sensitivity to Ca²⁺ is dependent on temperature.

Induction of sperm hypermotility through membrane progestin receptor alpha (mPRα): A teleost model of rapid, multifaceted, nongenomic progestin signaling

Rapid progestin effects on sperm physiology have been described in a variety of vertebrate species. Here, we briefly review the signaling pathways mediating rapid progestin induction of sperm hypermotility and increased fertility in two teleost species, Atlantic croaker and southern flounder. Acute in vitro treatment of teleost sperm with the progestin hormone, 20β-S, causes activation of progestin membrane receptor alpha (mPRα, or Paqr7) coupled to a stimulatory olfactory G protein (G_olf), resulting in increased cAMP and calcium concentrations and hypermotility upon activation in a hyperosmotic medium. Pharmacological tools were used to investigate the involvement of mPRα and several intracellular signaling pathways in the hypermotility response. Evidence was obtained using the specific mPRα agonist, Org OD 02-0, that this progestin action is mediated through mPRα and not through the nuclear PR. The results indicate that progestins induce hypermotility through activation of a membrane adenylyl cyclase (Acy)/cAMP pathway, an epidermal growth factor receptor (Egfr)/Mapkinase pathway, and a Pi3kinase/Akt/phosphodiesterase (Pde) pathway which result in increased sperm calcium concentrations within 10 s. The finding that inhibition of any one of these pathways is sufficient to prevent hypermotility along with the calcium increase suggests that activation of all of them and the associated calcium increase are required for the progestin hypermotility response. On the basis of these findings a model of progestin induction of sperm hypermotility in teleosts is proposed. As teleosts lack CatSper, the model described here is a non-CatSper mediated one and may therefore be applicable to a wide variety of nonmammalian vertebrates.

Sperm motility in fishes: (III) diversity of regulatory signals from membrane to the axoneme

Fish spermatozoa acquire potential for motility in the sperm duct where they are immotile. Osmolality of the seminal plasma is a key factor to maintain spermatozoa in the quiescent state in either freshwater or marine fishes. However, potassium (K⁺) ions prevent spermatozoa motility in salmonid and sturgeon fishes, while CO₂ inhibits spermatozoa motility in flatfishes. Once, spermatozoa are released at spawning, their motility is initiated in hypo-osmotic and hyper-osmotic environments in freshwater and marine fishes, respectively. Some substances produced by the testes (a progestin), or released from oocytes (peptides) induce spermatozoa hypermotility in some marine fishes including the Atlantic croaker and Pacific herrings, respectively. Duration of spermatozoa motility is short, lasting for a few seconds to few minutes in most fishes due to rapid depletion of energy required for the beating of the motility apparatus called axoneme. In the osmotic-activated spermatozoa, K⁺ and water effluxes occur in freshwater and marine fishes, respectively, which trigger spermatozoa motility signaling. In general, initiation of axonemal beating is associated with an increase in intracellular calcium (Ca²⁺) ions in spermatozoa of both freshwater and marine fishes and a post- or pre-increase in intracellular pH, while cyclic adenosine monophosphate (cAMP) remains unchanged. However, axonemal beating is cAMP-dependent in demembranated spermatozoa of salmonid and sturgeon fishes. Calcium from extracellular environment or intracellular stores supply required Ca²⁺ concentration for axonemal beating. Several axonemal proteins have been so far identified in fishes that are activated by Ca²⁺ and cAMP, directly or mediated by protein kinase C and protein kinase A, respectively. The present study reviews differences and similarities in complex regulatory signals controlling spermatozoa motility initiation in fishes, and notes physiological mechanisms that await elucidation.

Maladaptation of trout spermatozoa to fresh water is related to oxidative stress and proteome changes

Rainbow trout sperm are 'maladapted' to freshwater spawning, resulting in shorter duration of sperm motility in fresh water compared to buffered saline solution. We hypothesized that different sperm motility-activating media have various effects on sperm motility characteristics and oxidative stress, as well as on the protein profiles of rainbow trout sperm. We designed an experimental model for activation of rainbow trout sperm motility in different osmotic conditions: (i) isosmotic and (ii) hypoosmotic. Spermatozoa activation with hypoosmotic solution was associated with lower values for sperm motility parameters (52%) and an induced increase in ROS level (19.4%) in comparison to isosmotic activation with isosmotic solution (67 and 9.5% for sperm motility and ROS, respectively). Hypoosmotic activation resulted in a higher number of differentially abundant sperm proteins (out of which 50 were identified) compared to isosmotic conditions, where only two spots of protein disulfide-isomerase 6 were changed in abundance. The proteins are mainly involved in the TCA cycle, tight and gap junction signaling, Sertoli cell-Sertoli cell junction signaling and asparagine degradation. Our results, for the first time, indicate that during hypoosmotic activation of sperm motility, osmotic stress triggers oxidative stress and disturbances mostly to structural proteins and metabolic enzymes. Our results strongly suggest that comparative physiological and biochemical analysis of rainbow trout sperm characteristics in isosmotic and hypoosmotic conditions could be a useful model for studying the mechanism of sperm activation in salmonid fish.

Evaluation of seminal plasma composition and spermatozoa quality parameters of silver barb, Barbonymus gonionotus Bleeker, 1850

Seminal composition and semen quality are the important determinants in assessing the reproductive performance of different fishes. This study was carried out to evaluate the seminal composition and sperm quality of Barbonymus gonionotus. The seminal plasma contained 17.2 ± 0.34 mmol/l, 20.9 ± 0.48 mmol/l, 0.72 ± 0.04 mmol/l, 3.8 ± 0.2 mmol/l, and 1.49 ± 0.02 g/dl of Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, and total protein, respectively. The physical spermatological parameters, such as sperm volume, sperm motility, motility duration, sperm density, osmolality, and pH values were 1.55 ± 0.15 ml, 89 ± 2%, 391.9 ± 8.5 s, 2.8 ± 0.2 × 10¹⁰ /ml, 400.6 ± 5.1 mmol/kg, and 8.75 ± 0.10, respectively. In correlation matrix, the K⁺ (R² = 0.39, P < 0.01) and Ca⁺⁺ (R² = 0.27, P < 0.05) ions and osmolality (R² = 0.29, P < 0.05) showed significant positive correlations with sperm motility. Similarly, fertilization rate significantly influenced by sperm motility (R² = 0.26, P < 0.05) and K⁺ (R² = 0.30, P < 0.05) and Ca⁺⁺ (R² = 0.26, P < 0.05) ions. Also, osmolality significantly and negatively correlated with Mg⁺⁺ (R² = 0.33, P < 0.05) and sperm motility duration (R² = 0.28, P < 0.05). Therefore, based on this results, it can be concluded that seminal plasma ions, K⁺ and Ca⁺⁺ and osmolality are the key factors for the determination of sperm quality of silver barb, and these parameters could be considered during standardization of artificial fertilization or cryopreservation technique of silver barb spermatozoa.

Ovarian fluid impacts flagellar beating and biomechanical metrics of sperm between alternative reproductive tactics

Alternative reproductive tactics (ARTs) are prevalent in nature, where smaller parasitic males typically have better sperm quality than larger territorial guard males. At present, it is unclear what is causing this phenomenon. Our objective was to gain insights into sperm form and function by examining flagellar beating patterns (beat frequency, wave amplitude, bend length, bend angle, wave velocity) and biomechanical sperm metrics (velocity, hydrodynamic power output, propulsive efficiency) of wild spawning Chinook salmon ARTs. Ovarian fluid and milt were collected to form a series of eight experimental blocks, each composed of ovarian fluid from a unique female and sperm from a unique pair of parasitic jack and guard hooknose males. Sperm from each ART were activated in river water and ovarian fluid. Flagellar parameters were evaluated from recordings using high-speed video microscopy and biomechanical metrics were quantified. We show that ART has an impact on flagellar beating, where jacks had a higher bend length and bend angle than hooknoses. Activation media also impacted the pattern of flagellar parameters, such that beat frequency, wave velocity and bend angle declined, while wave amplitude of flagella increased when ovarian fluid was incorporated into activation media. Furthermore, we found that sperm from jacks swam faster than those from hooknoses and required less hydrodynamic power output to propel themselves in river water and ovarian fluid. Jack sperm were also more efficient at swimming than hooknose sperm, and propulsive efficiency increased when cells were activated in ovarian fluid. The results demonstrate that sperm biomechanics may be driving divergence in competitive reproductive success between ARTs.

Comparison of sperm motility subpopulation structure among wild anadromous and farmed male Atlantic salmon (Salmo salar) parr using a CASA system

Atlantic salmon (Salmo salar) is an endangered freshwater species that needs help to recover its wild stocks. However, the priority in aquaculture is to obtain successful fertilisation and genetic variability to secure the revival of the species. The aims of the present work were to study sperm subpopulation structure and motility patterns in wild anadromous males and farmed male Atlantic salmon parr. Salmon sperm samples were collected from wild anadromous salmon (WS) and two generations of farmed parr males. Sperm samples were collected from sexually mature males and sperm motility was analysed at different times after activation (5 and 35 s). Differences among the three groups were analysed using statistical techniques based on Cluster analysis the Bayesian method. Atlantic salmon were found to have three sperm subpopulations, and the spermatozoa in ejaculates of mature farmed parr males had a higher velocity and larger size than those of WS males. This could be an adaptation to high sperm competition because salmonid species are naturally adapted to this process. Motility analysis enables us to identify sperm subpopulations, and it may be useful to correlate these sperm subpopulations with fertilisation ability to test whether faster-swimming spermatozoa have a higher probability of success.

Effects of storage time on the motility, mortality and calcium levels of Atlantic salmon Salmo salar spermatozoa

This study estimates spermatozoa mortality, morphology, motility and intracellular calcium levels in Atlantic salmon Salmo salar milt after prolonged storage. Milt samples were preserved at 4° C for 25 days and then evaluated for mortality. Motility remained high for the first 3 days and the mortality was low during the first 5 days of storage. A decrease of >50% in calcium content was observed after 5 days of storage. When spermatozoa were activated, calcium levels increased >200% in relative fluorescence units (RFU); this rate of increase was lost when the samples were stored for extended periods of time and was only partially manifested in a zero calcium solution. The results suggest that in vitro storage of S. salar spermatozoa at 4° C for a period of 3 days preserves motility and limits mortality to levels similar to those of fresh spermatozoa. This method also maintains intracellular calcium storage critical for spermatozoa performance.

Chemical and physical guidance of fish spermatozoa into the egg through the micropyle†,‡

Eggs of teleost fish, unlike those of many other animals, allow sperm entry only at a single site, a narrow canal in the egg's chorion called the micropyle. In some fish (e.g., flounder, herring, and Alaska pollock), the micropyle is a narrow channel in the chorion, with or without a shallow depression around the outer opening of micropyle. In some other fish (e.g., salmon, pufferfish, cod, and medaka), the micropyle is like a funnel with a conical opening. Eggs of all the above fish have a glycoprotein tightly bound to the chorion surface around the micropyle. This glycoprotein directs spermatozoa into the micropylar canal in a Ca2+-dependent manner. This substance, called the micropylar sperm attractant or MISA, increases fertilization efficiency and is essential in herring. In flounder, salmon, and perhaps medaka, fertilization is possible without MISA, but its absence makes fertilization inefficient because most spermatozoa swim over the micropyle without entering it. The mechanism underlying sperm-MISA interactions is yet to be determined, but at least in herring the involvement of Ca2+ and K+ channel proteins, as well as CatSper and adenylyl cyclase, is very likely. In some other fish (e.g., zebrafish, loach, and goldfish), the chorion around the micropyle is deeply indented (e.g., zebrafish and loach) or it has radially or spirally arranged grooves around the outer opening of the micropyle (e.g., goldfish). MISA is absent from the eggs of these fish and sperm entry into micropylar canal seems to be purely physical.

Role of Ca2+ in the IVM of spermatozoa from the sterlet Acipenser ruthenus

The role of Ca2+ in sturgeon sperm maturation and motility was investigated. Sperm from mature male sterlets (Acipenser ruthenus) were collected from the Wolffian duct and testis 24 h after hormone induction. Testicular spermatozoa (TS) were incubated in Wolffian duct seminal fluid (WDSF) for 5 min at 20°C and were designated ‘TS after IVM’ (TSM). Sperm motility was activated in media with different ion compositions, with motility parameters analysed from standard video microscopy records. To investigate the role of calcium transport in the IVM process, IVM was performed (5 min at 20°C) in the presence of 2 mM EGTA, 100 µM Verapamil or 100 µM Tetracaine. No motility was observed in the case of TS (10 mM Tris, 25 mM NaCl, 50 mM Sucr with or without the addition of 2 mM EGTA). Both incubation of TS in WDSF and supplementation of the activation medium with Ca2+ led to sperm motility. The minimal Ca2+ concentration required for motility activation of Wolffian duct spermatozoa, TS and TSM was determined (1–2 nM for Wolffian duct spermatozoa and TSM; approximately 0.6 mM for TS). Motility was obtained after the addition of verapamil to the incubation medium during IVM, whereas the addition of EGTA completely suppressed motility, implying Ca2+ involvement in sturgeon sperm maturation. Further studies into the roles of Ca2+ transport in sturgeon sperm maturation and motility are required.

Motility of carp spermatozoa is associated with profound changes in the sperm proteome

In freshwater cyprinids, spermatozoa are quiescent in seminal plasma and sperm motility is initiated by a decrease in osmolality (hypo-osmotic shock) after discharge into the aqueous environment. However, it is unknown at present if and to what extent changes in proteins are involved in carp sperm motility. Therefore, the aim of our study was to identify proteins related to carp sperm motility through a comparison of immobilized and activated carp spermatozoa using a 2D-DIGE approach. Our results, for the first time indicated that carp sperm motility is associated with changes in protein content. Seventy-two differentially expressed proteins were identified. These proteins are mainly involved in ubiquitin-proteasome pathways, glycolysis, the TCA cycle, remodeling and are putatively related to sperm energy metabolism and motility. Moreover proteins associated with oxidative stress responses, signal transduction by Ca(2+)-dependent MAPK cascades, and PKC and protein folding have been identified. The proteins involved in carp sperm motility were localized to the cytoplasm, mitochondria, cytoskeleton, nucleus and sperm membrane. The identification of a high number of proteins involved in carp sperm motility would contribute to current knowledge about the molecular mechanisms of sperm motility in freshwater fish.

BIOLOGICAL SIGNIFICANCE

To the best of our knowledge, few changes in proteins involved in the initiation of fish sperm motility have been identified. This is a limited number of proteins compared with the 80 recently identified proteins involved in human sperm motility. However, no proteomic studies of sperm motility have yet been performed on freshwater fish. Our present study allowed for the first time a comprehensive characterization of the proteins associated with carp sperm motility and a better understanding of the molecular mechanisms underlying sperm motility activation and maintenance. The application of 2D-DIGE facilitated the identification proteins crucial for sperm structural organization and motility. The identification of a high number of proteins involved in carp sperm motility would contribute appreciably to the presently limited information available on the mechanisms of sperm motility in freshwater fish. Moreover the identified list of proteins will create a platform for future studies designed to assess the functional significance of specific proteins in sperm motility.

Role of calcium on the initiation of sperm motility in the European eel

Sperm from European eel males treated with hCGrec was washed in a calcium free extender, and sperm motility was activated both in the presence (seawater, SW) and in the absence of calcium (NaCl+EDTA), and treated with calcium inhibitors or modulators. The sperm motility parameters were evaluated by a computer-assisted sperm analysis (CASA) system, and changes in the [Ca(2+)]i fluorescence (and in [Na(+)]i in some cases) were evaluated by flow cytometry. After sperm motility was activated in a medium containing Ca(2+) (seawater, SW) the intracellular fluorescence emitted by Ca(2+) increased 4-6-fold compared to the levels in quiescent sperm. However, while sperm activation in a Ca-free media (NaCl+EDTA) resulted in a percentage of motility similar to seawater, the [Ca(2+)]i levels did not increase at all. This result strongly suggests that increasing [Ca(2+)]i is not a pre-requisite for the induction of sperm motility in European eel sperm. Several sperm velocities (VCL, VSL, VAP) decreased when sperm was activated in the Ca-free activator, thus supporting the theory that Ca(2+) has a modulatory effect on sperm motility. The results indicate that a calcium/sodium exchanger (NCX) which is inhibited by bepridil and a calcium calmodulin kinase (inhibited by W-7), are involved in the sperm motility of the European eel. Our results indicate that the increase in [Ca(2+)]i concentrations during sperm activation is due to an influx from the external medium, but, unlike in most other species, it does not appear to be necessary for the activation of motility in European eel sperm.

Aquaporin biology of spermatogenesis and sperm physiology in mammals and teleosts

Fluid homeostasis is recognized as a critical factor during the development, maturation, and function of vertebrate male germ cells. These processes have been associated with the presence of multiple members of the aquaporin superfamily of water and solute channels in different cell types along the reproductive tract as well as in spermatozoa. We present a comparative analysis of the existing knowledge of aquaporin biology in the male reproductive tissues of mammals and teleosts. Current data suggest that in both vertebrate groups, aquaporins may have similar functions during differentiation of spermatozoa in the germinal epithelium, in the concentration and maturation of sperm in the testicular ducts, and in the regulation of osmotically induced volume changes in ejaculated spermatozoa. Recent studies have also provided insight into the possible function of aquaporins beyond water transport, such as in signaling pathways during spermatogenesis or the sensing of cell swelling and mitochondrial peroxide transport in activated sperm. However, an understanding of the specific physiological functions of the various aquaporins during germ cell development and sperm motility, as well as the molecular mechanisms involved, remains elusive. Novel experimental approaches need to be developed to elucidate these processes and to dissect the regulatory intracellular pathways implicated, which will greatly help to uncover the molecular basis of sperm physiology and male fertility in vertebrates.

Coordinated Action of Aquaporins Regulates Sperm Motility in a Marine Teleost

In marine teleosts, such as the gilthead seabream, several aquaporin paralogs are known to be expressed during the hyperosmotic induction of spermatozoon motility in seawater. Here, we used immunological inhibition of channel function to investigate the physiological roles of Aqp1aa, Aqp1ab, and Aqp7 during seabream sperm activation. Double immunofluorescence microscopy of SW-activated sperm showed that Aqp1aa and Aqp7 were respectively distributed along the flagellum and the head, whereas Aqp1ab accumulated in the head and in discrete areas toward the anterior tail. Inhibition of Aqp1aa reduced the rise of intracellular Ca(2+), which is independent of external Ca(2+) and normally occurs upon activation, and strongly inhibited sperm motility. Impaired Aqp1aa function also prevented the intracellular trafficking of Aqp8b to the mitochondrion, where it acts as a peroxiporin allowing H2O2 efflux and ATP production during activation. However, restoring the Ca(2+) levels with a Ca(2+) ionophore in spermatozoa with immunosuppressed Aqp1aa function fully rescued mitochondrial Aqp8b accumulation and sperm motility. In contrast, exposure of sperm to Aqp1ab and Aqp7 antibodies did not affect motility during the initial phase of activation, but latently compromised the trajectory and the pattern of movement. These data reveal the coordinated action of spatially segregated aquaporins during sperm motility activation in a marine teleost, where flagellar-localized Aqp1aa plays a dual Ca(2+)-dependent role controlling the initiation of sperm motility and the activation of mitochondrial detoxification mechanisms, while Aqp1ab and Aqp7 in the head and anterior tail direct the motion pattern.

Inter-population ovarian fluid variation differentially modulates sperm motility in Atlantic cod Gadus morhua

This study tested the hypothesis that the effects of Atlantic cod Gadus morhua ovarian fluid on sperm motility variables are population specific. Sperm from a northern G. morhua population were activated in the presence of ovarian fluid from either northern or southern G. morhua at different concentrations. Ovarian fluid acted as a filter, in some cases reducing sperm swimming performance compared with seawater. Fluid from females foreign in population (southern) to the males (northern) had a greater inhibiting effect than those from the native population. Follow-up analysis indicated that the ovarian fluids had lower Ca(2+) concentration in northern than southern G. morhua, which could be the causative mechanism. If widespread, such cryptic female choice could reduce the incidence of intraspecific hybridization among diverged populations and contribute to reproductive isolation.

The role of Ca(2+) and Na (+) membrane transport in brook trout (Salvelinus fontinalis) spermatozoa motility

The role of environmental ion composition and osmolality in Ca(2+) signaled activation was assessed in spermatozoa of brook trout Salvelinus fontinalis. Milt from ten mature males was obtained by abdominal massage. Spermatozoa motility was evaluated in 0, 100, and 300 mOsm/kg NaCl or sucrose solutions, buffered by 10 mM Tris-HCl pH 8.5. For investigation of spermatozoa reaction to external Ca(2+) concentration, 2 mM ethylene glycol tetraacetic acid (EGTA) was added to the activation media as a calcium ions chelator. For investigation of the effect of external Na(+) concentration in conditions of low external Ca(2+), 100 µM amiloride was added to the EGTA-containing solutions as a Na(+) transport blocker. Low motility was observed in sucrose (Na(+) free) solutions containing 2 mM EGTA but not in Na(+) solutions containing 2 mM EGTA. Addition of amiloride led to significantly increased motility (P < 0.05) compared with sucrose (Na(+) free) solutions containing 2 mM EGTA. We conclude that Na(+) transport in Ca(2+)-free solutions plays a regulatory role in brook trout spermatozoa activation. The influence of competitive Na(+) and Ca(2+) transport on the control of spermatozoa activation requires further study with respect to its application for improvement of artificial activation and storage media.

Calcium ion supplementation increases brook trout Salvelinus fontinalis spermatozoa activation at the end of the spawning season

The role of environmental ion composition and osmolality in calcium ion (Ca(2+) ) signalling of spermatozoa activation over the course of the spawning period of brook trout Salvelinus fontinalis was investigated. Motility at the end of spawning was low (mean ± s.d. of 5 ± 2% motile spermatozoa with curvilinear velocity of 25 ± 8 µm s(-1) ). Addition of 10 mM Ca(2+) to the activation medium resulted in values similar to those recorded during the middle of the spawning period (mean ± s.d. of 95 ± 6% motile spermatozoa with curvilinear velocity of 130 ± 15 µm s(-1) ).

The effect of K(+), Ca (2+), and Mg (2+) on sperm motility in the perch, Perca fluviatilis

This study investigated the effect of 0.25-5 mM K(+), Ca(2+), and Mg(2+) on sperm motility in the perch, Perca fluviatilis. In 75 mM NaCl, the used motility-activating solution, motility rate, and swimming velocity decreased within the first 4 min after activation, and the rate of locally motile sperm increased. Thereafter, the motility parameters remained constant for periods >20 min. Based on the decrease in sperm motility, two types of semen samples could be distinguished. Semen samples of type I retained a high motility rate of >65 % after 20 min, and the rate of locally motile sperm was <20 %. In semen samples of type II, the motility rate decreased to values <30 % after 20 min, and the rate of locally motile sperm exceeded >50 %. Ca(2+) and Mg(2+) concentrations of 0.25-0.5 mM had no effect on the sperm motility parameters 10 s after activation, while 0.25 mM K(+) increased the swimming velocity. K(+), Ca(2+), and Mg(2+) concentrations ≥1.5 mM had suppressive effects on the sperm motility 10 s after activation. No differences were found between the two semen types. Twenty minutes after activation, type I semen was not affected by the tested cations. On the contrary, 0.25-2.5 mM K(+), 0.25 mM Mg(2+), and 0.25-2.5 mM Ca(2+) significantly increased the sperm motility rate and/or sperm velocity of type II semen. Therefore, supplementation of saline solution with cations might stabilize the motility of perch sperm, which can be a benefit for experimental purposes and for specific handling procedures in aquaculture.

Effect of pH and cation concentrations on spermatozoan motility of sea trout (Salmo trutta m. trutta L.)

Environmental conditions during external fertilization in fish have a significant effect on spermatozoan motility (MOT) and fertilization ability. Even in the same family of fish, spermatozoa might differ in sensitivity to ions present in the external medium. Elucidation of such differences within a species would help to understand spermatozoan biology and to determine external conditions that would optimize spermatozoan MOT and successful fertilization. Objectives of the current study were to determine the effects of pH and of sodium, potassium, and calcium ion concentrations in the activation solution on sea trout spermatozoan MOT. Six parameters characterizing MOT (MOT, curvilinear velocity [VCL], linearity, amplitude of lateral head displacement, beat cross frequency, and duration of MOT) in spermatozoa activated in prepared buffers were traced by computer-assisted sperm analysis. Sea trout spermatozoa were motile over a wide range of pH values, and increasing pH did influence MOT, VCL, linearity, amplitude of lateral head displacement, and MOT duration. The optimum pH for sperm MOT was established at approximately 10. Increasing K(+) ion concentration within the observed range caused a decrease in MOT and VCL. Spermatozoan movement ceased at 8 mM KCl concentrations. In Ca(2+) buffers, sperm were motile within the range of 0 to 70 mM CaCl(2) concentration; although beyond 8 mM concentration, VCL and MOT gradually declined. Spermatozoan aggregation was observed at the highest ion concentrations tested. Increasing CaCl(2) concentration affected MOT pattern from initiation to termination of spermatozoan movement in a similar manner as changes associated with increasing pH. At concentrations of CaCl(2) higher than 0.5 mM and in buffers with pH values 10 to 11, movement of spermatozoa was characterized by high initial linearity followed by its gradual reduction. In contrast to the effects of KCl and CaCl(2), increasing NaCl concentration up to 90 mM Na(+) concentration prolonged the duration of spermatozoan movement and, up to 60 mM Na(+) concentration, slightly increased sperm velocity as well. Above the concentration of 90 mM NaCl, these parameters decreased; and at 240 mM of Na(+), spermatozoa did not activate.

Transient Ca2+ mobilization caused by osmotic shock initiates salmonid fish sperm motility

Salmonid fish sperm motility is known to be suppressed in millimolar concentrations of extracellular K+, and dilution of K+ upon spawning triggers cAMP-dependent signaling for motility initiation. In a previous study, however, we demonstrated that suspending sperm in a 10% glycerol solution and subsequent dilution into a low-osmotic solution induced motility independently of extracellular K+ and cAMP. In the present study, we further investigated the glycerol-induced motility mechanism. We found that treatment with solutions consisting of organic or inorganic ions, as well as glycerol, induced sperm motility in an osmolarity-dependent manner. Elimination of intracellular Ca2+ by BAPTA-AM significantly inhibited glycerol-treated sperm motility, whereas removal of extracellular Ca2+ by EGTA did not. Monitoring intracellular Ca2+, using fluo-4, revealed that intracellular Ca2+ increased when sperm were suspended in hypertonic solutions, and a subsequent dilution into a hypotonic solution led to a decrease in intracellular Ca2+ concomitant with motility initiation. In addition, upon dilution of sperm into a hypertonic glycerol solution prior to demembranation, the motility of demembranated sperm was reactivated in the absence of cAMP. The motility recovery suggests that completion of axonemal maturation occurred during exposure to a hypertonic environment. As a result, it is likely that glycerol treatment of sperm undergoing hypertonic shock causes mobilization of intracellular Ca2+ from the intracellular Ca2+ store and also causes maturation of axonemal proteins for motility initiation. The subsequent dilution into a hypotonic solution induces a decrease in intracellular Ca2+ and flagellar movement. This novel mechanism of sperm motility initiation seems to act in a salvaging manner for the well-known K+-dependent pathway.

Identification of calcium-binding proteins in fish seminal plasma

Calcium ions play an important role in the activation of fish sperm movement. The mechanism of their binding in semen is still unknown. The goal of this study was the development of a method for identifying calcium-binding proteins in fish seminal plasma. Two methods of calcium-binding proteins detection were tested with the use of Quin2 and Stains-all dyes. The first method was useful for the identification of calcium-binding proteins of fish seminal plasma. It consisted of proteins separation using SDS-PAGE, transfer on PVDF membrane, incubation with CaCl₂, staining with Quin2 and illumination with UV light to reveal calcium-binding protein bands. Using Quin2 allowed the detection of calcium-binding proteins with low and high molecular weight. Electrophoretic species-specific profiles of calcium-binding proteins were identified in the seminal plasma of carp, whitefish, roach, brook trout, brown trout and rainbow trout. Staining of calcium-binding proteins with Quin2 is a quick and safe method, allowing the identification of calcium-binding proteins in fish semen.

Roles of osmolality, calcium - Potassium antagonist and calcium in activation and flagellar beating pattern of sturgeon sperm

The present study shows the roles of osmolality, calcium (Ca(2+))-potassium (K(+)) antagonist and Ca(2+) in sperm activation and flagellar beating of a sturgeon species, sterlet (Acipenser ruthenus). Sperm motility was activated at hypoosmolality relative to seminal plasma and suppressed at 175 mOsmol kg(-1). Sperm activation was totally suppressed by 0.35mM K(+), but Ca(2+) could fully reverse K(+) inhibitory effect at Ca(2+): K(+) ratio of 0.25. Neither EGTA (a chelator of Ca(2+) ions) nor nifedipine (a Ca(2+) channel blocker) prevented sperm activation. But, sperm motility and velocity were significantly decreased by EGTA, nifedipine and an inhibitor for Ca(2+)/calmodulin activated phosphodiesterase (w-7) that suggest role of Ca(2+) signaling after triggering sperm activation through hypoosmolality. Symmetric flagellar beating was also turned to asymmetric after activation in w-7, which is an evidence for modulation of Ca(2+)-binding proteins activity. Sturgeon sperm, similar to salmonids, is immotile in seminal plasma due to high K(+) concentrations, but the mechanism of sperm activation seems to be closer to other fish species where osmolality prohibits sperm activation in seminal plasma. In these species, hypoosmolality is the primary signal for sperm Ca(2+)-dependent signaling of axonemal beating.

Transmembrane adenylyl cyclase regulates amphibian sperm motility through protein kinase A activation

Sperm motility is essential for achieving fertilization. In animals with external fertilization as amphibians, spermatozoa are stored in a quiescent state in the testis. Spermiation to hypotonic fertilization media triggers activation of sperm motility. Bufo arenarum sperm are immotile in artificial seminal plasma (ASP) but acquire in situ flagellar beating upon dilution. In addition to the effect of low osmolarity on sperm motility activation, we report that diffusible factors of the egg jelly coat (EW) regulate motility patterns, switching from in situ to progressive movement. The signal transduction pathway involved in amphibian sperm motility activation is mostly unknown. In the present study, we show a correlation between motility activation triggered by low osmotic pressure and activation of protein kinase A (PKA). Moreover, this is the first study to present strong evidences that point toward a role of a transmembrane adenyl-cyclase (tmAC) in the regulation of amphibian sperm motility through PKA activation.

Sperm cryopreservation of the critically endangered olive barb (Sarpunti) Puntiussarana (Hamilton, 1822)

The present study focused on development of a sperm cryopreservation protocol for the critically endangered olive barb Puntiussarana (Hamilton, 1822) collected from two stocks within Bangladesh and reared in the Fisheries Field Laboratory, Bangladesh Agricultural University (BAU). The sperm were collected in Alsever's solution prepared at 296mOsmol kg(-1). Sperm were activated with distilled water (24mOsmol kg(-1)) to characterize motility. Maximum motility (90%) was observed within 15s after activation, and sperm remained motile for 35s. Sperm activation was evaluated in different osmolalities and motility was completely inhibited when osmolality of the extender was ≥287mOsmol kg(-1). To evaluate cryoprotectant toxicity, sperm were equilibrated with 5%, 10% and 15% each of dimethyl sulfoxide (DMSO) and methanol. Sperm motility was noticeably reduced within 10min, when sperm were equilibrated with 15% DMSO, indicating acute toxicity to spermatozoa and therefore this concentration was excluded in further trials. Sperm were cryopreserved using DMSO at concentrations of 5% and 10% and methanol at 5%, 10% and 15%. The one-step freezing protocol (from 5°C to -80°C at 10°C/min) was carried out in a computer-controlled freezer (FREEZE CONTROL® CL-3300; Australia) and 0.25-ml straws containing spermatozoa were stored in liquid nitrogen for 7-15days at -196°C. The highest motility in thawed sperm 61±8% (mean±SD) was obtained with 10% DMSO. The fertilization and hatching rates were 70% and 37% for cryopreserved sperm, and 72% and 62% for fresh sperm. The protocol reported here can be useful for hatchery-scale production of olive barb. The use of cryopreserved sperm can facilitate hatchery operations, and can provide for long-term conservation of genetic resources to contribute in the recovery of critically endangered fish such as the olive barb.

Effects of extracellular environment factors on the motility in Japanese eel spermatozoa

We have examined the effects in vitro of the ionic composition, pH and temperature on the motility by the spermatozoa of the Japanese eel (Anguilla japonica). Milt was obtained from 10 males that had been artificially matured by repeated injections of hCG. Sperm motility was monitored with a VHS video recorder and a video camera connected to a microscope. The results showed that most of the sperm were highly motile in 250-700 mM NaCl, 250-650 mM KCl and 350-550 mM CaCl2 solution. The longest duration of sperm motility recorded in 500 mM NaCl, 250 mM KCl and 350 mM CaCl2 solution. Sperm was not motile when suspended at pH 2, sperm motility was observed at pH 3, there was a relatively higher percentage of motile sperm in solutions at pH 4-12 (above 80%). The motility and duration increased within 18-24°C and decreased at the range of 24-30°C. Appropriate K+ ion concentration in the active medium could enhance the percent motility and duration of eel spermatozoa.

Semen biology of vendace (Coregonus albula L.)

The objective of this study was to describe the morphometry and motility parameters of vendace (Coregonus albula) spermatozoa. Morphometric parameters of vendace sperm head and tail were of values similar to rainbow trout. The effects of pH, sodium, potassium and calcium ion concentrations on computer-assisted sperm analysis (CASA) sperm motility characteristics were tested. Vendace sperm was motile in a wide pH range of 6.0-10.5 with the optimum pH established at 9.0. Increases in potassium and calcium ions caused decreases in the percentage of motile sperm. The CASA parameters and erratic sperm movement pattern of vendace spermatozoa were similar to whitefish (C. lavaretus) sperm motility, suggesting that there is a coregonid-specific sperm motility pattern.

Frenetic activation of fish spermatozoa flagella entails short-term motility, portending their precocious decadence

In most species, fish spermatozoa activate their motility on contact with the external medium (sea or fresh water depending of their reproductive habitat). Their flagella immediately develop waves propagated at high beat frequency (up to 70 beats s(-1)), which propel these sperm cells at high velocity (6-10 mm min(-1)), but for a quite short period of time, usually limited to minutes. Their specific inability to restore their energy content (mostly adenosine triphosphate) fast enough relatively to their high rate of energy consumption by flagellar contributes mainly to the activity arrest of motility, as the spermatozoa need to rely on early accumulated energy prior to activation. This review of the published data explains the present understanding of physico-chemical mechanisms by which flagellar motility is activated (mostly through osmotic and ionic regulation) and then propels sperm cells at speed. It aims also to describe the gradual arrest of their motility much of which occurs within a few minutes.

Molecular mechanisms determining sperm motility initiation in two sparids (Sparus aurata and Lithognathus mormyrus)

Molecular mechanisms involved in sperm motility initiation in two sparids (Sparus aurata and Lithognathus mormyrus) have been studied. Our comparative study demonstrates that osmolality is the key signal in sperm motility activation in both species, whereas K(+) and Ca(2+) do not have any role. The straight-line velocity that resulted, however, was significantly different when measured in sperm activated with non-ionic and/or calcium-free solutions with respect to that measured in seawater-activated sperm. In both species, motility initiation depends on cAMP-dependent protein phosphorylation. The phosphorylation/dephosphorylation patterns that resulted in gilthead and striped sea bream were quite different. In gilthead sea bream, the phosphorylated proteins have molecular weights of 174, 147, 138, 70, and 9-15 kDa, whereas the dephosphorylated proteins have molecular weights of 76, 57, and 33 kDa. In striped sea bream, phosphorylation after sperm motility activation occurred on proteins of 174, 147, 103, 96, 61, 57, and 28 kDa, whereas only one protein of 70 kDa resulted from dephosphorylation. Matrix-assisted laser desorption ionization-time of flight analyses allowed identification of the following proteins: In gilthead sea bream, the 9-15 kDa proteins that were phosphorylated after motility activation include an A-kinase anchor protein (AKAP), an acetyl-coenzyme A synthetase, and a protein phosphatase inhibitor, and in striped sea bream, 103- and 61-kDa proteins that were phosphorylated after motility activation were identified as a phosphatase (myotubularin-related protein 1) and a kinase (DYRK3), respectively.

Post-thaw amendment of cryopreserved sperm for use in artificial insemination of a viviparous fish, the green swordtail Xiphophorus helleri

Sperm cryopreservation protocols have been developed for live-bearers such as the green swordtail Xiphophorus helleri and the platyfish Xiphophorus couchianus. Despite the high post-thaw motility (~75%) obtained in both species, the requirements of sperm storage within the female reproductive tract coupled with the process of internal fertilization place functional demands upon cryopreserved sperm samples far beyond those of oviparous species. The purpose of this study was to facilitate the artificial insemination process with cryopreserved sperm of X. helleri through evaluation of parameters related to sperm quality after thawing. Specifically, this study evaluated the effects on motility for fresh and thawed sperm samples of centrifugation (for concentration of sperm and washing for removal of cryoprotectant), ionic composition, and additions of glucose and fetal bovine serum (FBS) in extender solutions. Centrifugation at 1000 ×g for 10 min at 4 °C was found to have no adverse effects on sperm motility of fresh samples, and for cryopreserved samples, the removal of glycerol by washing yielded higher and longer post-thaw motility (e.g., 168 h vs. 48 h for the controls). Suspension of fresh sperm samples in magnesium-free Hanks' balanced salt solution (HBSS) did not affect motility; however, HBSS prepared with the absence of potassium or calcium, and the use of unsupplemented saline (NaCl alone) as extenders significantly reduced sperm motility. The presence of glucose in HBSS yielded higher and longer motility for fresh and thawed samples, but addition of glucose at greater than 2 g/L were unnecessary. Addition of 20% FBS prior to freezing was found to increase the post-thaw motility significantly compared to control treatment with 14% glycerol alone. Also addition of 20% FBS after thawing and centrifugation was found to induce the formation of sperm bundles, which may be beneficial for internal fertilization success. In conclusion, concentration of sperm and the removal of cryoprotectant (through centrifugation), and the addition of 20% FBS in the extender is recommended for future insemination trials with cryopreserved samples.

Role of the Na+/Ca2+ exchanger in calcium homeostasis and human sperm motility regulation

A number of cell functions, such as flagellar beating, swimming velocity, acrosome reaction, etc., are triggered by a Ca2+ influx across the cell membrane. For appropriate physiological functions, the motile human sperm maintains the intracellular free calcium concentration ([Ca2+]i) at a submicromolar level. The objective of this study was to determine the role of the Na+/Ca2+ exchanger (NCX) in the maintenance of [Ca2+]i in human spermatozoa. Spermatozoa maintained in extracellular medium containing>or=1 microM Ca2+ exhibited motility similar to that of the control. In addition to several calcium transport mechanisms described earlier, we provide evidence that the NCX plays a crucial role in the maintenance of [Ca2+]i. Three chemically unrelated inhibitors of the NCX (bepridil, DCB (3',4'-dichlorobenzamil hydrochloride), and KB-R7943) all blocked human sperm motility in a dose and incubation time dependent manner. The IC50 values for bepridil, DCB, and KB-R7943 were 16.2, 9.8, and 5.3 microM, respectively. The treatment with the above-mentioned blockers resulted in an elevated [Ca2+]i and a decreased [Na+]i. The store-operated calcium channel (SOCC) inhibitor SKF 96365 also blocked the sperm motility (IC50=2.44 microM). The presence of the NCX antigen in the human spermatozoa was proven by flow cytometry, confocal laser scanning microscopy, and immunoblotting techniques. Calcium homeostasis of human spermatozoa is maintained by several transport proteins among which the SOCC and the NCX may play a major role.

Changes in sperm motility in response to osmolality/Ca2+ in three Indonesian fresh water teleosts: Goby (Oxyeleotris marmorata), Java carp (Puntius javanicus), and catfish (Clarias batrachus)

Sperm of most fresh water teleosts become motile when released into the hypotonic fresh water environment, but the role of osmolality and Ca2+ on sperm motility is not clear. Osmotic pressure and Ca2+ concentrations increase from fresh water to brackish water. Java carp Puntius javanicus and catfish Clarias batrachus live and reproduce only in fresh water. On the other hand, goby Oxyeleotris marmorata can acclimate and reproduce from fresh water to brackish water. In the present study, sperm motility and trajectory were compared among these three Indonesian endemic species. Sperm of Java carp, goby, and catfish begun to move in the hypotonic condition (< 200 mOsm/kg). However, the response to Ca2+ was different among these teleosts. In the presence of Ca2+, Java carp sperm swam in circular paths and immediately become quiescent, suggesting that Java carp sperm motility is activated in hypotonic aquatic environment without Ca2+. Goby sperm swam straightforward in the presence or absence of Ca2+. Percentages of motile sperm increased in 100-200 mOsm/kg but suppressed by removal of Ca2+. Regarding sperm motility and trajectory, no response was found in catfish sperm. These results suggest that a response to Ca2+ is different among sperm of the three species and suited to their habitat.

Initial studies on sperm cryopreservation of a live-bearing fish, the green swordtail Xiphophorus helleri

Swordtails and platyfish of the genus Xiphophorus are valuable models for biomedical research and are also commercially raised as ornamental fish valued by aquarists. While research use and commercial interest increases yearly in these fish, cryopreservation of sperm is unexplored in this genus. Xiphophorus are live-bearing fishes characterized by small body sizes, limited sperm volumes, and internal fertilization, an atypical reproductive mode for fish. These attributes make research involving cryopreservation of Xiphophorus germplasm challenging. To explore methods for sperm cryopreservation, this study evaluated the effect of different loading volumes of sperm suspension in 0.25-ml French straws, different dilution ratios of sperm to extender, an osmolality range of extender without cryoprotectant and with dimethyl sulfoxide (DMSO) as cryoprotectant, and short-term storage at room temperature and 4 degrees C after thawing. No significant difference in sperm motility due to straw loading volume was observed after thawing. Sperm motility was observed to decrease with increasing dilution. The osmolality of Hanks' balanced salt solution (HBSS) without cryoprotectant in which the highest sperm motility (67%) was observed was 320 +/- 3 mOsm/kg, which was also the osmolality of X. helleri blood plasma. When cryopreserved with 10% DMSO, however, the highest motilities within 10 min after thawing were observed with HBSS in the range of 240-300 mOsm/kg. Sperm suspended in HBSS at 320 mOsm/kg with a dilution factor of 100 maintained motility for 24h at room temperature, but persisted for 10 days when stored at 4 degrees C. These results provided the first evidence that cryopreservation may be applied to conservation of genetic resources in live-bearing fishes.

Activation of sperm motility in striped bass via a cAMP-independent pathway

The objective of the present study was to identify the effect of osmolality, ions (K+, H+, Ca2+, Mg2+) and cAMP on the initiation of sperm motility in striped bass (Morone saxatilis). Striped bass spermatozoa remained motile in solutions isotonic to seminal plasma (350 mOsm/kg) until osmolality reached 600 mOsm/kg. K+ (0-100 mM) had no effect ( p>0.05 ) on sperm motility, and sperm displayed a high percentage of motility over a wide range of pH (6.0-8.5). Sperm motility could be initiated in Ca2+-free solutions. In contrast, sperm motility was inhibited (P<0.01) by solutions containing > or =10 mM Ca2+, and sperm could not be reactivated by a Ca2+-free solution. This Ca2+ inhibition was not affected by verapamil, a Ca2+ channel blocker. However, if sperm motility was first initiated in a Ca2+-free solution, the addition of Ca2+ solutions, up to 80 mM, failed to inhibit sperm motility, suggesting that Ca2+ inhibited the initiation of motility, but had no control of motile spermatozoa. Mg2+ solutions had similar inhibitory effects on sperm motility as Ca2+ solutions. Therefore, initiation of motility in striped bass sperm may be related to voltage-gated channels across the cell's plasma membrane. Membrane permeable cAMP did not initiate motility of quiescent, intact striped bass spermatozoa, and motility of demembranated sperm could be activated in the absence of cAMP.

Acclimation of sperm motility apparatus in seawater-acclimated euryhaline tilapiaOreochromis mossambicus

Euryhaline tilapia Oreochromis mossambicus can reproduce in freshwater and in seawater. Regulation of sperm motility appears to be modulated during acclimation of the fish from freshwater to seawater, being independent of extracellular Ca2+ in freshwater and dependent on extracellular Ca2+ in seawater. In the presence of extracellular Ca2+, sperm of seawater-acclimated tilapia (SWT) showed motility even in a hypertonic environment, whereas sperm of freshwater-acclimated tilapia (FWT) were not motile. The Ca2+ indicator, fluo-3, revealed that intracellular Ca2+ concentration, [Ca2+]i, of SWT sperm increased only in the presence of extracellular Ca2+ in hypotonic or hypertonic conditions. Since the increased [Ca2+]i in FWT sperm occurred under hypotonic conditions via intracellular Ca2+ stores, it is likely that tilapia modulate their source of increasing [Ca2+]i from intracellular stores (in FWT sperm) to extracellular stores (in SWT sperm). Experiments using demembranated sperm revealed that Ca2+ is necessary for activation of motility,suggesting that Ca2+ plays a key role in motility regulation in SWT sperm. We detected three phosphoproteins associated with the activation of sperm motility. Serine and threonine residues of two proteins of 15 kDa and 18 kDa became dephosphorylated in hypotonic conditions but remained phosphorylated in hypertonic conditions, suggesting that these protein phosphorylations were not only related to motility activation under hypertonic conditions but also resistant to osmotic pressure. The threonine residue(s) of a 41 kDa protein was also phosphorylated in dry sperm, even in FWT sperm in motility-feasible hypotonic conditions. It is likely that acclimation of the motility apparatus is associated with modulation of the flow of Ca2+ to increase [Ca2+]i and protein phosphorylation.

Gadolinium, a mechano-sensitive channel blocker, inhibits osmosis-initiated motility of sea- and freshwater fish sperm, but does not affect human or ascidian sperm motility

Exposure to hypo-osmotic or hyperosmotic environment triggers the initiation of fish sperm motility. In this article, we report that calcium and potassium channel blockers do not influence motility of puffer fish sperm but calmodulin antagonists reversibly decrease it, suggesting that calmodulin-Ca(2+) interactions are prerequisite for the initiation of sperm motility in this species. Gadolinium (a stretch activated ion channel blocker) decreased the motility of puffer fish sperm from 92 +/- 3% to 6 +/- 3% and that of carp sperm from 91 +/- 7% to 3.5 +/- 4.3% in a dose-dependent manner (10-40 micro M). The effect of gadolinium was reversible, suggesting that stretch activated ion channels participate in the initiation of sperm motility of the two species. Gadolinium inhibits changes in the isoelectric point of certain proteins of puffer fish sperm, which occur when sperm motility is initiated in a hypertonic solution. Anisotropy measurements showed that hypo-osmotic treatment, which initiates carp sperm motility, increased membrane fluidity. When hypo-osmotic treatment was given in the presence of gadolinium, the sperm membrane remained as rigid as in quiescent cells, while motility was blocked. By contrast, gadolinium did not influence the motility parameters of Ciona or human sperm. Based on these lines of evidence, we suggest that conformational changes of mechanosensitive membrane proteins are involved in osmolality-dependent but not osmolality-independent sperm.

Requirement of Ca2+ on activation of sperm motility in euryhaline tilapia Oreochromis mossambicus

Euryhaline tilapia Oreochromis mossambicus acclimates to the external spawning environment by modulating its mechanism for regulating sperm motility. Adaptation of sperm was performed by acclimating fish in various environments. In this paper, regulatory mechanisms of freshwater-acclimated tilapia were studied in detail. Tilapia sperm motility was vigorous in hypotonic conditions and decreased with increasing osmolality. Sperm motility was reduced in hypotonic conditions when extracellular Ca(2+) was chelated; however, extracellular Ca(2+) was not a major factor for motility activation since sperm were motile even when extracellular Ca(2+) levels were nominally depleted by EGTA. The Ca(2+) indicator, fluo 3, showed that intracellular [Ca(2+)] increased on motility activation independently of extracellular [Ca(2+)], accompanied by swelling of the sperm neck region called the sleeve structure. Intracellular [Ca(2+)] was not increased under hypertonic conditions, in which sperm were immotile, even on addition of extracellular Ca(2+). It is possible that Ca(2+) is stored in the neck region. Demembranated sperm were reactivated in the presence of Ca(2+), but cAMP failed to reactivate the motility. Furthermore, we detected phosphorylation and dephosphorylation of three proteins at serine and threonine residues on motility activation. It is likely that hypotonic shock causes an increase in intracellular [Ca(2+)] that activates motility activation via phosphorylation of some flagellar proteins.

The use of phosphocreatine plus ADP as energy source for motility of membrane-deprived trout spermatozoa

Live trout spermatozoa initiate flagellar motility for a short period of time (30 s at 18 degrees C), during which their mean beat frequency (BF) decreases steadily from 60 to 20 Hz; motility then stops abruptly. When demembranated, the motility of axonemes lasts much longer, up to 20 min, with high beat frequency, provided that ATP (millimolar concentration) and cAMP (micromolar) are added. In the present paper, the motility of demembranated trout sperm was investigated in the absence of added ATP in various incubation conditions relative to other substrates. Without the addition of exogenous creatine kinase, the addition of phosphocreatine (PCr) and ADP shows the appearance of a progressive activation of all sperm models with BF increasing with time up to high values. Without the addition of cAMP, the BF increases to lower values but flagella propagated poorly coordinated waves for only a few min. Similar progressive activation is also observed when only ADP is added (without any previous in vivo activation) and BF increases up to moderate values. In this latter case, no activation occurs without addition of cAMP. The respective roles of creatine kinase and adenylate kinase in this process were investigated by addition of specific inhibitors such as fluorodinitrobenzene and P1,P5-di(adenosine-5')pentaphosphate in the above described conditions. We conclude from these observations that all the elements necessary for a coupling between ADP/PCr/creatine kinase on one hand and ATP/ADP/dynein on the other appear to be present in trout spermatozoa: thus the existence of a shuttle sustaining this coupling is strongly suggested.

Membrane hyperpolarization removes inactivation of Ca2+ channels, leading to Ca2+ influx and subsequent initiation of sperm motility in the common carp

Change of osmolality surrounding spawned sperm from isotonic to hypotonic causes the initiation of sperm motility in the common carp. Here we show that membrane-permeable cAMP does not initiate motility of carp sperm that is quiescent in isotonic solution, and that motility of the demembranated sperm can be reactivated without cAMP. Furthermore, the cAMP level does not change during the initiation of sperm motility, and inhibitors of protein kinase do not affect sperm motility, suggesting that no cAMP-dependent system is necessary for the regulation of sperm motility. Sperm motility could not be initiated in Ca(2+)-free hypoosmotic solutions, and significant increase in the intracellular Ca(2+) level was observed by a Ca-sensitive fluorescence dye during hypoosmolality-induced active motion period. The demembranated sperm cells were fully reactivated in the solutions containing 10(-7) to 10(-5) M Ca(2+). Ca(2+) channel blockers such as verapamil and omega-conotoxin reversibly inhibited the initiation of sperm motility, suggesting that Ca(2+) influx is the prerequisite for the initiation of carp sperm motility. Motility of intact sperm was completely blocked; however, that of the demembranated sperm was not inhibited by the calmodulin inhibitor W7, suggesting that the calmodulin bound close to the plasma membrane participated in the initiation of sperm motility. Flow cytometric membrane potential measurements and spectrophotometric measurements by using fluorescence dyes showed transient membrane hyperpolarization on hypoosmolality-induced motility. This article discusses the role of membrane hyperpolarization on removal of inactivation of Ca(2+) channels, leading to Ca(2+) influx at the initiation of carp sperm motility.

Release of Ca(2+) from intracellular stores and entry of extracellular Ca(2+) are involved in sea squirt sperm activation

A rise in intracellular free Ca(2+) concentration ([Ca(2+)](i)) is required to activate sperm of all organisms studied. Such elevation of [Ca(2+)](i) can occur either by influx of extracellular Ca(2+) or by release of Ca(2+) from intracellular stores. We have examined these sources of Ca(2+) in sperm from the sea squirt Ascidia ceratodes using mitochondrial translocation to evaluate activation and the Ca(2+)-sensitive dye fura-2 to monitor [Ca(2+)](i) by bulk spectrofluorometry. Sperm activation artificially evoked by incubation in high-pH seawater was inhibited by reducing seawater [Ca(2+)], as well as by the presence of high [K(+)](o) or the Ca channel blockers pimozide, penfluridol, or Ni(2+), but not nifedipine or Co(2+). The accompanying rise in [Ca(2+)](i) was also blocked by pimozide or penfluridol. These results indicate that activation produced by alkaline incubation involves opening of plasmalemmal voltage-dependent Ca channels and Ca(2+) entry to initiate mitochondrial translocation. Incubation in thimerosal or thapsigargin, but not ryanodine (even if combined with caffeine pretreatment), evoked sperm activation. Activation by thimerosal was insensitive to reduced external calcium and to Ca channel blockers. Sperm [Ca(2+)](i) increased upon incubation in high-pH or thimerosal-containing seawater, but only the high-pH-dependent elevation in [Ca(2+)](i) could be inhibited by pimozide or penfluridol. Treatment with the protonophore CCCP indicated that only a small percentage of sperm could release enough Ca(2+) from mitochondria to cause activation. Inositol 1,4,5-trisphosphate (IP(3)) delivered by liposomes or by permeabilization increased sperm activation. Both of these effects were blocked by heparin. We conclude that high external pH induces intracellular alkalization that directly or indirectly activates plasma membrane voltage-dependent Ca channels allowing entry of external Ca(2+) and that thimerosal stimulates release of Ca(2+) from IP(3)-sensitive intracellular stores.

Ion channels in sperm physiology

Fertilization is a matter of life or death. In animals of sexual reproduction, the appropriate communication between mature and competent male and female gametes determines the generation of a new individual. Ion channels are key elements in the dialogue between sperm, its environment, and the egg. Components from the outer layer of the egg induce ion permeability changes in sperm that regulate sperm motility, chemotaxis, and the acrosome reaction. Sperm are tiny differentiated terminal cells unable to synthesize protein and difficult to study electrophysiologically. Thus understanding how sperm ion channels participate in fertilization requires combining planar bilayer techniques, in vivo measurements of membrane potential, intracellular Ca2+ and intracellular pH using fluorescent probes, patch-clamp recordings, and molecular cloning and heterologous expression. Spermatogenic cells are larger than sperm and synthesize the ion channels that will end up in mature sperm. Correlating the presence and cellular distribution of various ion channels with their functional status at different stages of spermatogenesis is contributing to understand their participation in differentiation and in sperm physiology. The multi-faceted approach being used to unravel sperm ion channel function and regulation is yielding valuable information about the finely orchestrated events that lead to sperm activation, induction of the acrosome reaction, and in the end to the miracle of life.

Ultrastructural study of osmolality effect on spermatozoa of three marine teleosts

With particular emphasis on mitochondria that may provide endogenous energy for spermatozoan motility, the morphological changes of the spermatozoa of three marine teleosts, black porgy (Acanthopagrus schlegelli), black grouper (Epinephelus malabaricus), and Atlantic croaker (Micropogonias undulatus), were compared either after activation in artificial sea water or when immersed in various osmotic pressure media. The midpieces of these three teleosts spermatozoa are composed of mitochondria surrounding the flagellum. Each mitochondrion is enclosed by distinct outer and inner membranes. The inner membrane separates the organelle's volume into two phases: the matrix and the intermembrane space. The inner membrane displays numerous infolding cristae that vary in number and shape and extend into the matrix. Following activation with artificial sea water, spermatozoa became motile and both the size and number of mitochondria decrease and then totally disappear. The present study strongly suggests that an energy source(s), responsible for motility, is located within the mitochondria in the midpiece of these three marine teleost spermatozoa.