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

Role of voltage-gated L-type calcium channel in the spermatozoa motility of Atlantic salmon (Salmo salar)

Ca²⁺ cations play a key role in the initiation of spermatozoa motility in Atlantic salmon (Salmo salar). In this study we assess the importance of the voltage-gated L-type calcium channels in the spermatozoa motility of Atlantic salmon by combined in vitro and in silico approaches. The results of this study showed that as in other fish species, voltage-gated L-type calcium channels are significant in the spermatozoa motility of Salmo salar. The in vitro assays showed that total and progressive motilities decrease significantly (****p < .001) when Salmo salar spermatozoa are treated with verapamil, which has its binding site in the pore of the voltage-gated L-type calcium channel according to the in silico analysis.

Sperm motility in fish: technical applications and perspectives through CASA-Mot systems

Although a relatively high number of sperm quality biomarkers have been reported over the years in several fish species, sperm motility is nowadays considered the best biomarker for fish spermatozoa. The first scientific reports focusing on fish sperm motility date from a century ago, but the objective assessment allowed by computer-aided sperm analysis (CASA-Mot) systems was not applied to fish species until the mid-1980s. Since then, a high number of sperm kinetic parameters from more than 170 fish species have been reported in more than 700 scientific articles, covering a wide range of topics, such as sperm physiology, sperm storage, broodstock management, the phenomenon of sperm competition, ecotoxicology and understanding the life cycle of the species. The sperm kinetic parameters provided by CASA-Mot systems can serve as powerful and useful tools for aquaculture and ecological purposes, and this review provides an overview of the major research areas in which fish sperm motility assessment by a CASA-Mot system has been used successfully.

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.

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.

Optimum calcium concentration: a crucial factor in regulating sperm motility in vitro

Sperm motility can be maintained in vitro by incubation in a defined medium under specific conditions. In most studies, the exact role of various constituents of epididymal fluid, including calcium, has remained obscure. Most of the culture media have included millimolar concentrations of calcium, but previous reports have indicated that millimolar calcium inhibits sperm motility. In this present study, we sought the optimum concentration of extracellular calcium required for optimum sperm motility. This study showed that extracellular calcium has a concentration-dependent biphasic role in motility regulation. It promoted motility and velocity at lower (10 µM) concentration whereas notably inhibited it at higher concentrations. When external membrane-bound calcium was removed by ethylene glycol tetraacetic acid, motility decreased considerably. To confirm the motility-inhibiting role of calcium above 10 µM, a sperm motility-stimulating protein (MSP) recently reported from our laboratory was used which at 0.9 μM induces motility in 60-70 % cells. Calcium at 10 µM had no appreciable effect on the motility-promoting activity of the MSP but depressed the activity above 10 µM. Thus, our present results emphasize the biphasic role of extracellular calcium and the importance of its optimum concentration in different buffers and media used for sperm motility initiation.

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.