Glycerol permeability of human spermatozoa and its activation energy

Problems of human spermatozoa cryopreservation: research methods, solutions

Cryopreservation of male gametes is one of the most important methods of assisted reproductive technologies, which allows preserving gametes for research or further use. However, the fertilizing ability of spermatozoa after cryopreservation decreases by 30-70%, which makes it urgent to search for new substances with cryoprotective properties. The review considers the main causes of cell damage during cryopreservation. The relevance of methods for assessing the formation of crystals and the physicochemical properties of cryoprotective media depending on various compositions is discussed. The problem of stabilization of the spermatozoa membrane during cryopreservation is considered. A possible solution to the problem of membrane integrity may consist in modification of the basic cryoprotective media with yolk emulsion or development of methods for saturation of the membrane phospholipid layer with cholesterol.

Aquaporin-7-Mediated Glycerol Permeability Is Linked to Human Sperm Motility in Asthenozoospermia and during Sperm Capacitation

Osmoregulation plays a vital role in sperm function, encompassing spermatogenesis, maturation, and fertilization. Aquaglyceroporins, a subclass of aquaporins (AQPs), facilitate the transport of water and glycerol across the sperm membrane, with glycerol serving as an important substrate for sperm bioenergetics. This study aimed to elucidate the significance of AQP-mediated glycerol permeability in sperm motility. The presence and localization of AQP3 and AQP7 in human sperm were assessed using immunofluorescence. Subsequently, the glycerol permeability of spermatozoa obtained from normozoospermic individuals (n = 30) was measured, using stopped-flow light scattering, after incubation with specific aquaporin inhibitors targeting AQP3 (DFP00173), AQP7 (Z433927330), or general aquaglyceroporin (phloretin). Sperm from asthenozoospermic men (n = 30) were utilized to evaluate the AQP7-mediated glycerol permeability, and to compare it with that of normozoospermic men. Furthermore, hypermotile capacitated sperm cells were examined, to determine the AQP7 expression and membrane glycerol permeability. AQP3 was predominantly observed in the tail region, while AQP7 was present in the head, midpiece, and tail of human sperm. Our findings indicate that AQP7 plays a key role in glycerol permeability, as the inhibition of AQP7 resulted in a 55% decrease in glycerol diffusion across the sperm membrane. Importantly, this glycerol permeability impairment was evident in spermatozoa from asthenozoospermic individuals, suggesting the dysregulation of AQP7-mediated glycerol transport, despite similar AQP7 levels. Conversely, the AQP7 expression increased in capacitated sperm, compared to non-capacitated sperm. Hence, AQP7-mediated permeability may serve as a valuable indicator of sperm motility, and be crucial in sperm function.

Spermatozoa from the maned wolf (Chrysocyon brachyurus) display typical canid hyper-sensitivity to osmotic and freezing-induced injury, but respond favorably to dimethyl sulfoxide

We assessed the influences of medium osmolality, cryoprotectant and cooling and warming rate on maned wolf (Chrysocyon brachyurus) spermatozoa. Ejaculates were exposed to Ham's F10 medium (isotonic control) or to this medium plus NaCl (350-1000mOsm), sucrose (369 and 479mOsm), 1M glycerol (1086mOsm) or dimethyl sulfoxide (Me2SO, 1151mOsm) for 10 min. Each sample then was diluted back into Ham's medium and assessed for sperm motility and plasma membrane integrity. Although glycerol and Me2SO had no influence (P>0.05), NaCl and sucrose solutions affected sperm motility (P<0.05), but not membrane integrity. Motility of sperm exposed to <600mOsm NaCl or sucrose was less (P<0.05) than fresh ejaculate, but comparable (P>0.05) to the control. As osmolality of the NaCl solution increased, motility decreased to <5%. In a separate study, ejaculates were diluted in Test Yolk Buffer containing 1M glycerol or Me2SO and cooled from 5°C to -120°C at -57.8°C, -124.2°C or -67.0°C/min, frozen in LN2, thawed in a water bath for 30s at 37°C or 10s at 50°C, and then assessed for motility, plasma- and acrosomal membrane integrity. Cryopreservation markedly (P<0.05) reduced sperm motility by 70% compared to fresh samples. Higher (P<0.05) post-thaw motility (20.0±1.9% versus 13.5±2.1%) and membrane integrity (51.2±1.7% versus 41.5±2.2%) were observed in samples cryopreserved in Me2SO than in glycerol. Cooling rates influenced survival of sperm cryopreserved in glycerol with -57.8°C/min being advantageous (P<0.05). The findings demonstrate that although maned wolf spermatozoa are similar to domestic dog sperm in their sensitivity to osmotic-induced motility damage, the plasma membranes tolerate dehydration, and the cells respond favorably to Me2SO as a cryoprotectant.

Suprazero cooling rate, rather than freezing rate, determines post thaw quality of rhesus macaque sperm

Sperm become most sensitive to cold shock when cooled from 37 °C to 5 °C at rates that are too fast or too slow; cold shock increases the susceptibility to oxidative damage owing to its influence on reactive oxygen species (ROS) production, which are significant stress factors generated during cooling and low temperature storage. In addition, ROS may be a main cause of decreased motility and fertility upon warming. They have been shown to change cellular function through the disruption of the sperm plasma membrane and through damage to proteins and DNA. The objective of this study was to determine which cryopreservation rates result in the lowest degree of oxidative damage and greatest sperm quality. In the rhesus model, it has not been determined whether suprazero cooling or subzero freezing rates causes a significant amount of ROS damage to sperm. Semen samples were collected from male rhesus macaques, washed, and resuspended in TEST-yolk cryopreservation buffer to 100 × 10(6) sperm/mL. Sperm were frozen in 0.5-mL straws at four different combinations of suprazero and subzero rates. Three different suprazero rates were used between 22 °C and 0 °C: 0.5 °C/min (slow), 45 °C/min (medium), and 93 °C/min (fast). These suprazero rates were used in combination with two different subzero rates for temperatures 0 °C to -110 °C: 42 °C/min (medium) and 87 °C/min (fast). The different freezing groups were as follows: slow-med (SM), slow-fast (SF), med-med (MM), and fast-fast (FF). Flow cytometry was used to detect lipid peroxidation (LPO), a result of ROS generation. Motility was evaluated using a computer assisted sperm motion analyzer. The MM and FF treated sperm had less viable (P < 0.0001) and motile sperm (P < 0.001) than the SM, SF, or fresh sperm. Sperm exposed to MM and FF treatments demonstrated significantly higher oxidative damage than SM, SF, or fresh sperm (P < 0.05). The SM- and SF-treated sperm showed decreased motility, membrane integrity, and LPO compared with fresh semen (P < 0.001). Slow cooling from room temperature promotes higher membrane integrity and motility post thaw, compared with medium or fast cooling rates. Cells exposed to similar cooling rates with differing freezing rates were not different in motility and membrane integrity, whereas comparison of cells exposed to differing cooling rates with similar freezing rates indicated significant differences in motility, membrane integrity, and LPO. These data suggest that sperm quality seems to be more sensitive to the cooling, rather than freezing rate and highlight the role of the suprazero cooling rate in post thaw sperm quality.

[Assisted reproductive technologies with sperm donation]

INTRODUCTION

The purpose of this review is to relate to the operating rules of CECOS in France and the legal, medical and ethical issues raised by sperm donation.

MATERIAL AND METHODS

Review of articles and consensus conferences on this subject published in Medline (PubMed) selected from 1973 and 2011 according to their relevance and Acts recorded on official legislative French websites.

RESULTS

The operating rules of CECOS were established by the Act of July 29, 2004, revised 6 August 2004 and July 7, 2011. Of the 21,759 children born of ART in France in 2009, 5.1% are from a sperm donation. From 1973 to 2006, 44,045 children are born after a sperm donation. Between 1973 and 2006, 16,971 donors are presented in the CECOS and only 10,347 donors have completely made their donation process. The main indication for use of donor sperm (75% of applications) is represented by men of infertile couples with nonobstructive azoospermia, the second indication is infertile men with oligospermia. In azoospermia, the application is usually performed after failure of testicular or epididymal surgical specimen. In oligozoospermia, claims made most often after several failures of intraconjugal ART.

CONCLUSION

Many questions are still present around the conception of children by sperm donation. The legitimacy of maintaining anonymity in the gift remains widely debated.

Multistep and single-step treatment of human spermatozoa with cryoprotectants

OBJECTIVE

To compare the impact of multi- and single-step addition of cryoprotectants on human spermatozoa.

DESIGN

Human semen was subjected to cryoprotective agents (CPAs) in both one-step and multistep protocols before removal of the CPAs by multi-step and single-step methods.

SETTING

Infertility clinic.

PATIENT(S)

Healthy normozoospermic volunteers.

INTERVENTION(S)

Single- and multistep addition and removal of a range of CPAs.

MAIN OUTCOME MEASURE(S)

Analysis of tail morphology and total and progressive motility, as well as kinematic parameters, in medium and sperm penetration into artificial mucus.

RESULT(S)

While no CPA drastically affected sperm vitality, some were more deleterious than others. Propane-1,3-diol was the least damaging to sperm function, whereas glycerol and ethyl(hydroxymethyl)propane were particularly disruptive. For all CPAs, multistep addition and removal of CPAs proved less damaging to sperm function than the single-step protocol.

CONCLUSION(S)

Optimal CPAs may be those that minimize osmotic stresses to spermatozoa during prefreeze and post-thaw procedures.

Resistance to osmotic stress of horse spermatozoa: the role of ionic pumps and their relationship to cryopreservation success

To study the resistance of horse spermatozoa against hyperosmotic stress, cells were incubated in solutions of 600 to 4000 mOsm(undisturbed media). Then, semen was immediately placed into an iso-osmotic solution (disrupted media). Incubation in undisturbed media decreased sperm viability in an osmolarity- and temperature-dependent manner. Viability was further decreased in disrupted media, with the effect dependent upon the initial osmolarity of the media and on the temperature. Treatment with ouabain or amiloride impaired the resistance of horse spermatozoa to hyperosmotic stress. Very few correlations were strong between viability after hyperosomotic stress and quality parameters of fresh and frozen-thawed horse semen. The results indicate that the usefulness of resistance to hyperosmotic stress in assessing frozen-thawed semen quality is compromised, since other factors are involved in the resistance to freezing-thawing. Both Na (+)K (+) ATP-ase and the Na (+)H (+) antiporter act in the resistance to hyperosmotic stress in horse spermatozoa.

Activation of Caspases in Human Spermatozoa during Cryopreservation – An Immunoblot Study

Cellular stress to ejaculated spermatozoa such as cryopreservation is known to induce caspase-derived, apoptotic signaling. Therefore, the proenzymes and active forms of caspases 1, 3, 8 and 9 were examined by western blot technique in unfrozen and frozen human spermatozoa of infertility patients and of healthy donors. Twenty-two semen samples derived from healthy donors and 26 semen samples of unselected infertility patients were divided into 3 parts, two of them were cryostored at -196 degrees C with 7% or 14% (v/v, final concentration) of glycerol. The caspases were detected by immunoblots with polyclonal rabbit-anti-caspases-antibodies after 15% sodium dodecyl sulfate-polyacrylgel electrophoresis (SDS-PAGE) under reducing conditions. For evaluation of the differences between amounts of caspase protein the luminol/H(2)O(2) method was applied. A significant increase of activated caspase-1 in donors, of caspase-8 in patients and caspase-9 in patients and donors after cryopreservation were found, whereas, the application of 14% glycerol resulted in higher amounts of activated caspase than did 7% glycerol. Possibly, glycerol may also contribute to activation of caspases via direct toxic effects to mitochondria during cryopreservation of spermatozoa. This finding strongly supports an hypothesis of a higher mitochondria-derived apoptosis-sensitivity of spermatozoa in patients than in healthy donors during cryopreservation. Inactive caspase-3 was reduced subsequent to cryopreservation in patients (p<0.05) and non-significant in donors (p<0.05). Active caspase-3 was detectable in all samples but without significant differences between the three assays. It is concluded that mechanisms associated with apoptotic processes deserve attention in cryopreservation of spermatozoa in order to conserve vital sperm functions after thawing.

Cryoprotectant permeation through human articular cartilage

OBJECTIVE

The cryopreservation of intact articular cartilage is constrained by minimal chondrocyte survival. It was the aim of the present study to gain an insight into the permeation kinetics of cryoprotectants through cartilage. This knowledge is essential for achieving adequate tissue permeation prior to cooling.

DESIGN

The diffusion coefficients and penetration rates through human articular cartilage of dimethyl sulfoxide (Me(2)SO) and glycerol at different temperatures (4 degrees C, 17 degrees C, 27 degrees C and 37 degrees C) and at two concentrations [10% (v/v) and absolute state] were measured using diffusion nuclear magnetic imaging. Deuterated water (D(2)O) was used as a control substance.

RESULTS

Glycerol penetrated faster than Me(2)SO at all temperatures and at rates that were comparable to those for D(2)O. The penetration rate of each agent increased with increasing temperature. The diffusion coefficients for glycerol and Me(2)SO increased with increasing temperature and decreased at the higher concentration, but the differences between each agent were not significant.

CONCLUSIONS

The classical cryopreservation protocols expose cartilage samples to Me(2)SO at a too low temperature and/or for an insufficient time period for optimal cell survival. When considering the penetration rate, glycerol appears to be a more efficient cryoprotective agent than Me(2)SO. The present study demonstrates the power of nuclear magnetic resonance technology to elucidate key physiological factors in cryobiology.

Fundamentals of cryobiology in reproductive medicine

The aim of this review will be to provide a basic understanding of the biophysical processes that accompany the application of cryopreservation in reproductive medicine. The ability to store cells in 'suspended animation' outside the body has become a keystone practice in the development of many modern clinical therapies, and, in fact, the sciences of cryobiology and IVF have developed in parallel over the past 50 years. During this time, some of the underlying principles of the quantitative biophysical aspects of cryobiology have been clarified. Water is the universal biocompatible solvent, but also possesses unique properties for stability of living cells. Whilst low temperatures themselves have defined effects on cell structure and function, it is the phase transition of water to ice that is the most profound challenge for survival. The thermodynamics of dilute aqueous solutions dictate how cells and tissues respond to the freezing process. Current concepts of nucleation, ice crystal growth and solute exclusion from the ice lattice will be discussed to illustrate what cells must negotiate to avoid lethal damage, and the role of cryoprotectants in enhancing recovery. Quantitative formalisms now exist to model and predict how water and solutes move across cell membranes before and during freezing, or how nucleation events will proceed, and these will be outlined. Cryoprotectants have both positive and negative effects on cell function depending on the kinetics of exposure. The concept of tolerable osmotic excursion of cell volume will be discussed, along with the evidence for a 'pseudo-glassy' state for cells during traditional cryopreservation. This will be compared with the recent interest in promoting glassy states in the whole sample using vitrification protocols, outlining the advantages and drawbacks of each approach. Additional methods for controlling ice nucleation have a role to play here, and a brief outline of current technologies will be given. Finally, issues of safety and stability of cryopreserved samples will be set out.

Osmotic tolerance of equine spermatozoa and the effects of soluble cryoprotectants on equine sperm motility, viability, and mitochondrial membrane potential

Osmotic stress attributed to differences in the relative permeability of cryoprotectants, such as glycerol and water, appears to be an important factor in cryodamage. The objective of this study was to characterize the osmotic tolerance of equine spermatozoa, and to evaluate the effects of addition and removal of cryoprotectants from equine spermatozoa on their motility, and membrane and acrosomal integrity, as well as their mitochondrial membrane potential. Equine spermatozoa had a limited osmotic tolerance to anisosmotic conditions. Although the addition of increasing concentrations of glycerol decreased the motility and viability of equine spermatozoa, the rapid removal of glycerol by dilution in isosmotic media resulted in an even greater decline in motility and viability compared with spermatozoa maintained under anisosmotic conditions. Likewise, the addition and rapid removal of 1.0 M glycerol, ethylene glycol, dimethylsulfoxide, or propylene glycol resulted in a significant decline in sperm motility and viability. Among these cryoprotectants, ethylene glycol had the least detrimental effect on either viability or motility of spermatozoa following the rapid addition and removal of these cryoprotectants. These data demonstrate that equine spermatozoa have a limited osmotic tolerance compared with published reports for mouse or human spermatozoa, and appear to be more similar to boar spermatozoa in their osmotic tolerance. Of the 4 cryoprotectants evaluated in equine spermatozoa, the addition and removal of glycerol resulted in a more marked osmotic stress as indicated by alterations in motility, viability, and acrosomal integrity. These data suggest that alternative cryoprotectants should be considered for cryopreservation of equine spermatozoa in order to reduce osmotic stress associated with the addition of these agents during semen freezing.

Effects of Equex, one- or two-step dilution, and two freezing and thawing rates on post-thaw survival of dog spermatozoa

The objectives of the present study were to evaluate the effects of adding Equex to a TRIS-extender, diluting the semen in 1 or 2 steps, freezing according to 2 methods, thawing at 2 rates, and the interactions between these treatments, on the post-thaw survival of dog spermatozoa at 38 degrees C. Ten ejaculates were obtained from 8 dogs. Each ejaculate was centrifuged, and the seminal plasma was discarded. Each sperm pellet was diluted with 2 mL of a TRIS-glucose-egg yolk extender containing 3% glycerol (Extender 1 [Ext-1]). Ejaculates were then pooled (9 x 10(9) spermatozoa), and Ext-1 was added to obtain 200 x 10(6) spermatozoa/mL. The semen pool was carefully mixed and divided into aliquots, and processed according to a 2 x 2 x 2 x 2 factorial design to evaluate the effects of 1) adding the same volume of a second TRIS-glucose-egg yolk extender with 7% glycerol that contained (Ext-2-E) or didn't contain (Ext-2) 1% of Equex STM Paste (final concentration of spermatozoa 100 x 10(6) spermatozoa/mL, glycerol 5%, Equex 0% [Ext-2] or 0.5% [Ext-2-E]); 2) diluting the semen in 1 step (adding Ext-2 or Ext-2-E before equilibration) or in 2 steps (adding Ext-2 or Ext-2-E after equilibration, just before the freezing operation); 3) freezing the straws horizontally in a styrofoam box 4 cm above liquid nitrogen (LN2) or by lowering them vertically into a LN2 tank in 3 steps; and 4) thawing at 70 degrees C for 8 sec or at 37 degrees C for 15 sec. A total of 16 treatment combinations were evaluated. Sperm motility was evaluated after thawing and at 1-h intervals during 7 h of incubation at 38 degrees C by subjective examination and by using a CASA-system. Plasma membrane integrity and acrosomal status were evaluated simultaneously at 1, 3 and 6 h post-thaw using a triple fluorescent staining procedure and flow cytometry. The best post-thaw survival and thermoresistance of spermatozoa was obtained when Equex was present in the extender (P<0.0001); the semen dilution was performed in 2 steps instead of 1 (P<0.0001); the freezing was carried out using the box instead of the tank (P<0.05); and the straws were thawed at 70 degrees C for 8 sec instead of at 37 degrees C for 15 sec (P<0.0001).

Species variation in osmotic, cryoprotectant, and cooling rate tolerance in poultry, eagle, and peregrine falcon spermatozoa

Potential factors influencing spermatozoa survival to cryopreservation and thawing were analyzed across a range of the following avian species: domestic chicken (Gallus domesticus), domestic turkey (Meleagris gallopavo), golden eagle (Aquila chrysaetos), Bonelli's eagle (Hieraaetus fasciatus), imperial eagle (Aquila adalberti), and peregrine falcon (Falco peregrinus). Studies focused on spermatozoa tolerance to the following: 1) osmotic stress, 2) different extracellular concentrations of the cryoprotectant dimethylacetamide (DMA), 3) equilibration times of 1 versus 4 h, 4) equilibration temperature of 4 versus 21 degrees C, and 5) rapid versus slow cooling before cryopreservation and standard thawing. Sperm viability was assessed with the live/dead stain (SYBR-14/propidium iodine). Sperm viability at osmolalities >/=800 mOsm was higher (P: < 0.05) in raptor than poultry semen. Return to isotonicity after exposure to hypertonicity (3000 mOsm) decreased (P: < 0.05) number of viable spermatozoa in chicken, turkey, and golden and Bonelli's eagle spermatozoa but not in imperial eagle or peregrine falcon spermatozoa. Differences were found in spermatozoa resistance to hypotonic conditions, with eagle species demonstrating the most tolerance. Semen, equilibrated for 1 h (4 degrees C) in diluent containing DMA (> or =2.06 M), experienced decreased (P: < 0. 05) spermatozoa survival in all species, except the golden eagle and peregrine falcon. Number of surviving spermatozoa diminished progressively with increasing DMA concentrations in all species. Increased equilibration temperature (from 4 to 21 degrees C) markedly reduced (P: < 0.05) spermatozoa survival in all species except the Bonelli's eagle and turkey. Rapid cooling was detrimental (P: < 0.05) to spermatozoa from all species except the imperial eagle and the chicken. These results demonstrate that avian spermatozoa differ remarkably in response to osmotic changes, DMA concentrations, equilibration time, temperature, and survival after fast or slow freezing. These differences emphasize the need for species-specific studies in the development and enhancement of assisted breeding for poultry and endangered species.

Centrifugation and addition of glycerol at 22 degres C instead of 4 degrees C improve post-thaw motility and fertility of stallion spermatozoa

The aims of this study were to evaluate the effects of cooling rate to 4 degrees C and temperature at the time of centrifugation/glycerol-addition (freezing extender: INRA82 + 2% egg yolk + 2.5% glycerol) on postcentrifugation recovery rate, post-thaw motility and per-cycle fertility. When centrifugation/glycerol-addition was performed at 4 degrees C (14 ejaculates), a moderate cooling rate (37 degrees C to 4 degrees C in I h) resulted in higher post-thaw motility (45%) than when using a slow cooling rate (37 degrees C to 4 degrees C in 4 h) (39%; P<0.05). When centrifugation/glycerol-addition was performed at 22 degrees C (37 degrees C to 22 degrees C in 10 min) (10 ejaculates), post-thaw motility was lower when spermatozoa were frozen directly from 22 degrees C (23%) than when spermatozoa were cooled to 4 degrees C (22 degrees C to 4 degrees C in 1 h) before freezing (47%; P<0.0001). When centrifugation/glycerol-addition was performed at 22 degrees C (before cooling at a moderate rate), as opposed to 4 degrees C (after cooling at a moderate rate), a significant improvement of 1) recovery of spermatozoa after centrifugation (P<0,0001), 2) post-thaw motility of spermatozoa at thawing (40% vs 36% (n < or = 291 ejaculates/group), P<0.0001) and 3) per-cycle fertility (56% vs 42% (n > or = 190 cycles/group), P<0.01) was observed. In conclusion, centrifugation/glycerol-addition at 22 degrees C followed by cooling to 4 degrees C at a moderate rate results in an improvement of post-thaw motility, spermatozoa recovery rate and per cycle fertility.

Basic aspects of frozen storage of semen

Basic concepts of cryopreservation and the causes of cryoinjury are reviewed. The possible roles of cryoprotectants and additives are considered in the context of their putative interactions with the sperm plasma membrane. Modern approaches to the laboratory assessment of spermatozoa after freeze-thawing are also briefly discussed.

Fundamental aspects of sperm cryobiology: the importance of species and individual differences

While semen cryopreservation is successfully used for a few species, application to other species can be problematic. Here, I argue that species differences in female tract anatomy, subtle differences in sperm transport mechanisms, ability to time inseminations and deliver spermatozoa effectively are powerful determinants of fertility with cryopreserved spermatozoa. Poor sperm survival represents one major aspects of the problem and determining biophysical characteristics of the sperm plasma membrane is an established approach to solving it. However, this approach is unable to account for the consistent differences in post-cryopreservation sperm quality between individual males, an effect that is recognized is many species although only documented in a few. Searching for genetic differences between these individuals might offer a genomically-based direction in semen cryopreservation research. Cryopreservation of spermatozoa and spermatogenic cells for intracytoplasmic sperm injection has been developed primarily to deliver an intact genome and presents a very different set of technical problems.

Hydraulic conductivity (Lp) and its activation energy (Ea), cryoprotectant agent permeability (Ps) and its Ea, and reflection coefficients (sigma) for golden hamster individual pancreatic islet cell membranes

Long-term cryopreservation of islets of Langerhans would be advantageous to a clinical islet transplantation program. Fundamental cryobiology utilizes knowledge of basic biophysical characteristics to increase the understanding of the preservation process and possibly increase survival rate. In this study several of these previously unreported characteristics have been determined for individual islet cells isolated from Golden hamster islets. Using an electronic particle counting device and a temperature control apparatus, dynamic volumetric response of individual islet cells to anisosmotic challenges of 1.5 M dimethyl sulfoxide (DMSO) and 1.5 M ethylene glycol (EG) were recorded at four temperatures (8, 22, 28, and 37 degreesC). The resulting curves were fitted using Kedem and Katchalsky equations which describe water flux and cryoprotectant agent (CPA) flux based on hydraulic conductivity (Lp), CPA permeability (Ps), and reflection coefficient (final sigma) for the membrane. For Golden hamster islet cells, Lp, Ps, and final sigma for DMSO at 22 degreesC were found to be 0.23 +/- 0.06 microm/min/atm, 0.79 +/- 0.32 x 10(-3) cm/min, and 0.55 +/- 0.37 (n = 11) (mean +/- SD), respectively. For EG at 22 degreesC, Lp equaled 0.23 +/- 0.06 microm/min/atm, Ps equaled 0.63 +/- 0.20 x 10(-3) cm/min, and final sigma was 0.75 +/- 0.17 (n = 9). Arrhenius plots (ln Lp or ln Ps versus 1/temperature (K)) were created by adding the data from the other three temperatures and the resulting linear regression yielded correlation coefficients (r) of 0.99 for all four plots (Lp and Ps for both CPAs). Activation energies (Ea) of Lp and Ps were calculated from the slopes of the regressions. The values for DMSO were found to be 12.43 and 18.34 kcal/mol for Lp and Ps (four temperatures, total n = 52), respectively. For EG, Ea of Lp was 11.69 kcal/mol and Ea of Ps was 20.35 kcal/mol (four temperatures, total n = 58).

Survival of bull sperm frozen at different rates in media varying in osmolarity

The effects of freezing procedures, osmolarity, trehalose, and sucrose on survival of bull sperm in whole milk (WM) and egg yolk-Tris (EYT), semen extenders used worldwide, were studied. Sperm were added to extenders at 25 degreesC, cooled slowly to 5 degreesC, glycerolated, packaged in 0.5-ml straws, and frozen. Different freezing rates were accomplished in two steps. Straws were transferred from +5 degreesC to nitrogen vapor at temperatures ranging from -10 to -100 degreesC in the first step and to liquid nitrogen in the second step. Straws were thawed in water at 35 degreesC. A substantial decrease in sperm motility occurred between -10 and -20 degreesC, as abrupt nucleation occurred following supercooling to -13 degreesC. To study the interactions between osmolarity x cooling rate, WM and EYT extenders were prepared to yield media measuring 220 to 420 mOsm/L. The optimal first-step range of cooling in the two-step procedure was -30 to -70 degreesC, and the highest proportions of motile sperm after freezing and thawing were 61 to 62 in 260 to 300 mOsm/L WM and 63 to 64% in 300 to 340 mOsm/L EYT, equivalent to the results with the control procedure used commercially. As the cooling rate increased (first step to -100 degreesC) sperm motility was much higher in hypertonic than in hypotonic extenders (P < 0.05), indicating the importance of partial dehydration before rapid cooling. Replacing part of EYT and WM with equivalent solutions (same mOsm/L) of sucrose or trehalose had no appreciable effect. These results provide a basis for further investigating simple freezing systems that might be more effective in preserving bull sperm than those currently available.

The determination of membrane permeability coefficients of canine pancreatic islet cells and their application to islet cryopreservation

Sufficient numbers of pancreatic islets for successful allotransplantation can be achieved by storing and then pooling islets from several donors. Optimal MHC matching and infectious disease screening also require long-term storage of islets, and cryopreservation is currently the only practical approach. Cryopreservation protocols may be optimized by modeling the changes in cell volume and the associated damage incurred during cryoprotectant addition and dilution and during cooling and warming. The objective of the present work was to determine the following biophysical parameters of canine islet cells; the osmotically inactive cell volume (Vb), hydraulic conductivity (Lp), cryoprotectant permeability coefficient (Ps), and the reflection coefficient sigma. A determination of these parameters allows the simulation of cell responses using computer models. Islets were isolated by collagenase digestion and Euro-Ficoll purification. After 24 h culture, islets were dissociated into single cells using trypsin and 2 mM EGTA. The kinetic change in cell volume as a function of time after exposure to 2 M dimethyl sulfoxide (Me2SO) was measured using an electronic particle counter at 22, 5, and -3 degrees C. At -11 degrees C, cells were preloaded with 1 M Me2SO and exposed to 4 M Me2SO to prevent the formation of ice in the working solution. Kedem-Katchalsky theory was used to describe the cell volume change kinetics, and a three-parameter curve fitting was performed using the Marquardt-Levenberg method to determine Lp, Ps, and sigma values. The Lp was determined to be 0.19 +/- 0.05, 0.037 +/- 0.005, 0.020 +/- 0.003, and 0.013 +/- 0.005 micron.min-1.atm-1 (mean +/- SD) at 22, 5, -3, and -11 degrees C, respectively. The Ps values were 1.05 +/- 0.50, 0.15 +/- 0.04, 0.096 +/- 0.028, and 0.067 +/- 0.029 x 10(-3) cm.min-1 at 22, 5, -3, and -11 degrees C, respectively. The sigma values were 0.81 +/- 0.16, 0.91 +/- 0.09, 0.80 +/- 0.21, and 0.98 +/- 0.04 at 22, 5, -3, and -11 degrees C, respectively. The temperature dependence or activation energy of Lp and Ps was calculated, using the Arrhenius equation, to be 12.7 and 13.5 kcal.mol-1, respectively. These permeability parameters were used to calculate cell water loss and the likelihood of lethal intracellular freezing during cooling, as well as both water flux and solute concentration gradients across the cell membrane during warming.

Resistance to hyperosmotic stress in boar spermatozoa: the role of the ionic pumps and the relationship with cryosurvival

The resistance to changes in the osmolarity of boar sperm was used to measure the resistance of boar sperm cells against freezing/thawing. Semen was incubated for 5 min in different solutions ranging from about 600 mOsm to about mOsm, and at 4 degrees C, 16 degrees C or 37 degrees C (undisturbed media). This undisturbed media was constituted by NaCl, glycerol or glucose. This semen was then placed in an isoosmotic solution (disrupted solutions). Incubation in undisturbed media did not alter the percentages of viability or altered acrosomes, except when the initial incubation has been at 37 degrees C and with osmolarities above 1000 mOsm. Viability and altered acrosome statistics were strongly modified in disrupted media. These effects are dependent upon the initial osmolarity of the media, but not upon the temperature. Pre-incubation with ouabain or amiloride did not affect spermatozoa incubated at 16 degrees C in a 2211 mOsm, NaCl medium. However, in sperm incubated in this 2211 mOsm medium and then rapidly placed in an isoosmotic solution, ouabain induced a decrease in viability and an increase in altered acrosomes. Amiloride did not affect the response of cells to the disrupted medium. Some significant correlations were observed among the percentages of altered acrosomes after hyperosmotic stress and some quality parameters of the fresh boar semen, especially the motion parameters. Although the resistance to hyperosmotic stress could be a valuable parameter in assessing fresh quality analysis, its usefulness in frozen-thawed semen is compromised, since other factors beside osmotic changes are involved in the resistance of boar semen to freezing-thawing. The NA+/K+, ouabain-dependent ATP-ase activity seems to be related to the mechanisms of resistance to hyperosmotic stress in boar sperm.

Frozen-thawed bovine spermatozoa diluted by slow or rapid dilution method: Measurements on occurrence of osmotic shock and sperm viability

This study was undertaken to investigate the occurrence of osmotic shock, sperm viability and membrane functional status of frozen-thawed bovine spermatozoa during a short-term incubation period (2 h) in vitro after dilution by 2 methods. Frozen semen from 10 bulls (0.5-ml plastic straws, 7% glycerol) was thawed and diluted by slow or rapid dilution method with Ham's F-10 medium containing 0 or 7% glycerol and assessed for sperm motion parameters, percentage of spermatozoa with coiled tails and reactivity to the hypoosmotic swelling (HOS; percentage of spermatozoa swelling) test at 60 min intervals during a 2 h incubation period (37 degrees C). Post-thaw sperm viability, as reflected by percentage and grade of motility (0 to 4) did not differ between the 2 dilution methods (P > 0.05) at the beginning of incubation (Time 0). However, differences were apparent (P < 0.05) as the incubation time increased. Slow dilution with medium containing 0% glycerol caused less increase (P < 0.05) in percentage of spermatozoa with coiled tails; Moreover, these spermatozoa showed greater reactivity to the HOS test. When contrasting slow vs rapid dilution methods, the occurrence of osmotic shock was less frequent, and response to the HOS test was greater for spermatozoa diluted slowly, regardless of the glycerol content of the incubation medium. Rapid deglycerolization of frozen-thawed bovine spermatozoa in a single step, induces damage which is not detected on the basis of spennatozoal motility but is clearly evident after several hours of incubation by using the HOS test to detect damage.

Human spermatozoa glycerol permeability and activation energy determined by electron paramagnetic resonance

The permeability of human spermatozoa to glycerol and its activation energy were determined using electron paramagnetic resonance (EPR) techniques. EPR was used to monitor the aqueous cell volume change vs. time during the glycerol permeation process using the aqueous spin label 15N-tempone and the membrane impermeable broadening agent potassium trioxalatochromiate (chromium oxalate). The permeation process was completed in tens of seconds, requiring the use of a stopped-flow methodology. The glycerol permeability coefficient (Pg) was determined by fitting a simple theoretical model to the experimental data. The permeabilities of human spermatozoa in 1 molar and 2 molar glycerol at 20 degrees C are (10.3 +/- 0.3).10(-4) cm/min (mean +/- S.D.) and (6.0 +/- 1.4).10(-4) cm/min, respectively. The permeabilities of human spermatozoa in 2 molar glycerol at 30, 20, 10, and 0 degrees C are (8.3 +/- 1.3).10(-4) cm/min, (6.0 +/- 1.4).10(-4) cm/min, (2.1 +/- 0.4).10(-4) cm/min, and (1.1 +/- 0.3).10(-4) cm/min, respectively. The activation energy (Ea) for glycerol permeation between 30 degrees C and 0 degrees C was found to be 11.6 kcal/mol.