Carbon dioxide and pH affect sperm motility of white sturgeon(Acipenser transmontanus)

Progesterone and anandamide diminish the inhibitory effect of zinc on mature human sperm

Zinc ion (Zn2+) homeostasis is very important for sperm capacitation and hyperactivation. Zn2+ is a specific inhibitor of the voltage-dependent proton channel (Hv1). Intracellular alkalisation of human spermatozoa is mainly dependent on opening of Hv1. Anandamide may affect spermatozoa through activation of Hv1. An increase in intracellular pH and progesterone (P4) activate cation channels of spermatozoa (CatSper). This study was designed to elucidate the interaction between ZnCl2, P4 and anandamide on human sperm function and intracellular calcium concentrations ([Ca2+]i). Human normal semen samples (n = 30) were diluted (20 × 106 spermatozoa mL-1) and divided into control and ethanol (0.01%)-, anandamide (1 nM)-, ZnCl2 (1 mM)-, P4 (10µM)-, anandamide+ZnCl2- and P4+ZnCl2-treated groups. Sperm kinematics, viability, acrosome status and [Ca2+]i were assessed. The percentage of viable and motile spermatozoa and sperm velocity was reduced in the ZnCl2-treated groups. Anandamide and P4 attenuated the inhibitory effects of ZnCl2 on sperm kinematics. Loss of the acrosome membrane was observed in all experimental groups. P4 and anandamide are present naturally in secretions of the female reproductive tract and modulate the inhibitory effects of ZnCl2 on sperm kinematics. This attenuation is probably due to a change in [Ca2+]i and prevention of Hv1 inactivation by P4 and anandamide respectively.

Adult exposure to acidified seawater influences sperm physiology in Mytilus galloprovincialis: Laboratory and in situ transplant experiments

The ongoing increase of CO₂ in the atmosphere is inducing a progressive lowering of marine water pH that is predicted to decrease to 7.8 by the end of this century. In marine environment, physical perturbation may affect reproduction, which is crucial for species' survival and strictly depends on gamete quality. The effects of seawater acidification (SWAc) on gamete quality of broadcast spawning marine invertebrates result largely from experiments of gamete exposure while the SWAc impact in response to adult exposure is poorly investigated. Performing microcosm and in field experiments at a naturally acidified site, we investigated the effects of adult SWAc exposure on sperm quality parameters underlying fertilization in Mytilus galloprovincialis. These animals were exposed to pH 7.8 over 21 days and collected at different times to analyze sperm parameters as concentration, motility, viability, morphology, oxidative status, intra- and extra-cellular pH and mitochondrial membrane potential. Results obtained in the two experimental approaches were slightly different. Under field conditions, we found an increase in total sperm motility and mitochondrial membrane potential on days 7 and 14 from the start of SWAc exposure whereas, in microcosm, SWAc group showed an increase of total motility on day 14. In addition, sperm morphology and intracellular pH were affected in both experimental approaches; whereas oxidative stress was detected only in spermatozoa collected from mussels under natural SWAc. The overall analysis suggests that, in mussels, SWAc toxic mechanism in spermatozoa does not involve oxidative stress. This study represents the first report on mussel sperm quality impairment after adult SWAc exposure, which may affect fertilization success with negative ecological and economic consequences; it also indicates that, although naturally acidified areas represent ideal natural laboratories for investigating the impact of ocean acidification, microcosm experiments are necessary for examining action mechanisms.

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.

Impact of environmental hypercapnia on fertilization success rate and the early embryonic development of the clam Limecola balthica (Bivalvia, Tellinidae) from the southern Baltic Sea - A potential CO2 leakage case study

Carbon capture and storage technology was developed as a tool to mitigate the increased emissions of carbon dioxide by capture, transportation, injection and storage of CO₂ into subterranean reservoirs. There is, however, a risk of future CO₂ leakage from sub-seabed storage sites to the sea-floor sediments and overlying water, causing a pH decrease. The aim of this study was to assess effects of CO₂-induced seawater acidification on fertilization success and early embryonic development of the sediment-burrowing bivalve Limecola balthica L. from the Baltic Sea. Laboratory experiments using a CO₂ enrichment system involved three different pH variants (pH 7.7 as control, pH 7.0 and pH 6.3, both representing environmental hypercapnia). The results showed significant fertilization success reduction under pH 7.0 and 6.3 and development delays at 4 and 9 h post gamete encounter. Several morphological aberrations (cell breakage, cytoplasm leakages, blastomere deformations) in the early embryos at different cleavage stages were observed.

Multiple aspects of male germ cell development and interactions with Sertoli cells require inositol hexakisphosphate kinase-1

Inositol hexakisphosphate kinase-1 (IP6K1) is required for male fertility, but the underlying mechanisms have been elusive. Here, we report that IP6K1 is required for multiple aspects of male germ cell development. This development requires selective interactions between germ cells and Sertoli cells, namely apical ectoplasmic specialization. Spermiation (sperm release) requires tubulobulbar complexes. We found that the apical ectoplasmic specialization and tubulobulbar complexes were poorly formed or disrupted in IP6K1 KOs. Deletion of IP6K1 elicited several aberrations, including: 1, sloughing off of round germ cells; 2, disorientation and malformation of elongating/elongated spermatids; 3, degeneration of acrosomes; 4, defects in germ-Sertoli cell interactions and 5, failure of spermiation. Eventually the sperm cells were not released but phagocytosed by Sertoli cells leading to an absence of sperm in the epididymis.

Antibiotics and oxygen availability affect the short-term storage of spermatozoa from the critically endangered booroolong frog, Litoria booroolongensis

Sperm-storage technologies aim to extend sperm longevity and increase the time available to achieve artificial fertilisation. The aim of the present study was to quantify the effects of antibiotic supplementation (4mgmL(-1) gentamicin) and altered gaseous storage environment (100%, 20% and 0% O2) on sperm longevity in the critically endangered booroolong frog, Litoria booroolongensis. A split-sample experimental design was adopted, whereby each sperm suspension (n=10) was evenly divided among six experimental treatments (100% O2 with antibiotic, 20% O2 with antibiotic, 0% O2 with antibiotic, 100% O2 without antibiotic, 20% O2 without antibiotic, 0% O2 without antibiotic). Sperm suspensions were refrigerated at 5°C for the duration of the 21-day storage period. Percentage sperm motility and sperm velocity were quantified every 3 days using a computer-assisted sperm analysis system. Treatments aerated with either 100% or 20% oxygen, without the addition of the antibiotic gentamicin, consistently exhibited the highest percentage sperm motility. On Day 21 of storage, sperm suspensions in these two treatments (100% O2 without antibiotic, 20% O2 without antibiotic) maintained 61.3% and 52.0% sperm motility, respectively, whereas all remaining experimental treatments exhibited <30% sperm motility. Sperm velocity did not differ significantly among storage treatments, at any of the sampling periods, with the exception of day 21. Overall, the results from this study indicate that increased oxygen availability is beneficial to sperm longevity, but that gentamicin inhibits sperm motility in L. booroolongensis.

Physiological impacts of elevated carbon dioxide and ocean acidification on fish

Most fish studied to date efficiently compensate for a hypercapnic acid-base disturbance; however, many recent studies examining the effects of ocean acidification on fish have documented impacts at CO2 levels predicted to occur before the end of this century. Notable impacts on neurosensory and behavioral endpoints, otolith growth, mitochondrial function, and metabolic rate demonstrate an unexpected sensitivity to current-day and near-future CO2 levels. Most explanations for these effects seem to center on increases in Pco2 and HCO3− that occur in the body during pH compensation for acid-base balance; however, few studies have measured these parameters at environmentally relevant CO2 levels or directly related them to reported negative endpoints. This compensatory response is well documented, but noted variation in dynamic regulation of acid-base transport pathways across species, exposure levels, and exposure duration suggests that multiple strategies may be utilized to cope with hypercapnia. Understanding this regulation and changes in ion gradients in extracellular and intracellular compartments during CO2 exposure could provide a basis for predicting sensitivity and explaining interspecies variation. Based on analysis of the existing literature, the present review presents a clear message that ocean acidification may cause significant effects on fish across multiple physiological systems, suggesting that pH compensation does not necessarily confer tolerance as downstream consequences and tradeoffs occur. It remains difficult to assess if acclimation responses during abrupt CO2 exposures will translate to fitness impacts over longer timescales. Nonetheless, identifying mechanisms and processes that may be subject to selective pressure could be one of many important components of assessing adaptive capacity.

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.

Sperm motility adaptation to ion-differing aquatic environments in the Tanganyikan cichlid, Astatotilapia burtoni

The cichlid fish, Astatotilapia burtoni, can acclimate and reproduce in both the K(+)-, Na(+)-, and Ca(2+)-rich waters of Lake Tanganyika (pH 8.9-9.2) and the surrounding rivers where K(+), Na(+), and Ca(2+) concentrations are low (pH 6.5). In this study, we compared sperm motility features among A. burtoni inhabiting the lake, those living in the surrounding rivers, and those from rivers that acclimates to lake water. Sperm of all three groups required extracellular Ca(2+) ([Ca(2+)]o) for sperm motility activation. However, involvement of K(+) and Na(+) were different. In sperm motility initiation of lake population, the decrease in Na(+) and increase in K(+) concentrations corresponding to a decrease in [Na(+)]o/[K(+)]o was required. In contrast, sperm motility in both the river population and those acclimated to lake water were activated only by a decrease in [Na(+)]o, suggesting that motility initiation cues regarding Na(+) and K(+) are different among populations within same species. One probable reason why the difference of initiation cues is that the concentration of K(+) in the river water (40 mM) is lower than that in the lake water (110 mM). These results suggest that sperm flagellar activation cascades of river and lake populations within this species differ as a result of adaptations to different ionic environments.

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.

Influence of osmolality and ions on the activation and characteristics of zebrafish sperm motility

Despite the prevalence of zebrafish as a model scientific organism, understanding sperm function in this species is essentially limited to observations that osmotic shock initiates motility. During natural spawning, sperm encounter a range of environmental salinities as well as freshwater mixed with egg-associated ovarian fluid (OF), thus sperm are likely to be exposed to saline prior to egg contact. Effects of saline on sperm function in this model species are unknown, but likely to be important. Using computer assisted sperm analysis, this study addressed the effects of osmolality of spawning media and ionic composition and pH on the proportion of sperm becoming motile at activation (motility), as well as sperm velocity and path. When activated with tap water, motility was maximal (80%) at 10s (earliest time measured), declining to 5% by 87 s postactivation. With activation at moderate osmolalities ( approximately 160-200 mmol/kg) initial motility was decreased relative to low osmolality, increased from 10 to 30s, and subsequently declined less rapidly (motility in 80 mM NaCl was 35%, 80%, and 60% at 10, 30 and 147 s, respectively). Thus, moderate osmolality increased duration, but introduced a temporal lag in motility onset. With moderate osmolalities, the rate of velocity decay was less than that with tap water activation. Sodium chloride and sucrose similarly impacted both motility and velocity. Replacement of NaCl with KCl, pH values ranging from 6.8 to 8.4, or the presence of gadolinium were without effect. Motility, but not velocity, was slightly supressed by Ca(2+). Therefore, whereas pH and concentrations of Ca(2+) or K(+) of OF are unlikely to impact fertility via sperm motility, the OF contribution to spawning media osmolality may have pronounced effects on motility and velocity of sperm, factors previously correlated with fertility in other species.

Do sperm contribute to the buffering capacity of steelhead trout (Oncorhynchus mykiss) semen?

The motility of salmonid sperm is pH-sensitive and the buffering capacity of the seminal plasma is low. The objective of the present study was to determine the extent to which sperm contribute to the buffering capacity of whole steelhead (Oncorhynchus mykiss) semen. To determine the buffering capacity, semen and seminal plasma samples were titrated with HCl and pH measurements taken at 1-2 min. The buffering capacity of semen was not different from that of seminal plasma over the pH range 7.5 to 8.5 and was approximately 15% to 20% less over the range 6.0 to 7.0. Comparable results were obtained for the semen and seminal plasma of the chinook salmon (Oncorhynchus tshawytscha). To assess whether the intracellular environment could influence the buffering capacity, the effects of cell disruption with n-butanol and Triton X-100 (TX-100) were determined. Over the pH range 7.5 to 8.5, the presence of n-butanol or TX-100 resulted in a doubling of the buffering capacity of the semen; TX-100, but not n-butanol, increased semen buffering capacity over the pH range 6.0 to 7.0. To determine whether the sperm's intracellular compartment might contribute to the buffering capacity over a longer duration, semen and seminal plasma samples were acidified with HCl and the pH measured over several hours. These data suggest that intact sperm contribute no more than about 25% to the buffering capacity of whole semen. The buffering capacity of steelhead semen and seminal plasma were comparably and modestly temperature sensitive. The results suggest that the sperm may contribute to the buffering capacity of the semen over a physiological pH range, however, if so, the effect is relatively small.

Spermatozoa motility in the Persian sturgeon, Acipenser persicus: effects of pH, dilution rate, ions and osmolality

Sperm motility is a prerequisite factor determining semen quality and fertilizing capacity. The effects of environmental factors including pH, cations and osmolality as well as the role of dilution rate on sperm motility parameters inAcipenser persicuswere studied. The best pH and dilution rate for activation of spermatozoa were pH 8.0 and dilution ratio 1:50. Ionic factors can stimulate the initiation of sperm activation. The maximum percentage of motile sperm and total duration of sperm motility were observed in solutions containing 25 mM NaCl, 0.2 mM KCl, 3 mM CaSO4, 10 mM MgSO4and sucrose with an osmolality of 50 mosmol kg−1. The present study provides us with some basic knowledge about sturgeon spermatozoa biosensitivity to ionic and osmolality effects. A sensitivity ofA. persicussperm was observed after induction of activation of sperm motility in solution containing cations or sucrose with high osmolality. Concentrations more than 50 mM Na+, more than 1 mM K+, more than 3 mM Ca2+and more than 10 mM Mg2+had negative effects on sperm motility. Also, osmolality more than 100 mosmol kg−1had an inhibitory effect. It is clear that ions and osmolality stimulate the motility of spermatozoa by changes in the properties of the plasma membrane including its potential and its ionic conductance. The inhibitory role of high osmolality of the swimming medium (more than 100 mosmol kg−1) and insufficient osmolality of the seminal plasma to inhibit semen motility suggested that osmolality is not the principal factor preventing sperm motility in seminal fluid but that K+is a major inhibitory factor of sperm motility in seminal plasma.