Site of freeze-thaw damage and cryoprotection by amino acids of the calcium ATPase of sarcoplasmic reticulum

A brief review of the methodology and cryoprotectants in selected fish and mammalian species

Cryopreservation is a valuable technique used to assist in the genetic improvement of cultured stocks and provide a continuous supply of good-quality semen for artificial insemination. Conserving semen by cryopreservation serves several purposes (e.g. artificial reproductive technologies and species conservation) and is also used in the clinical treatment of human infertility. However, the lifespan of cryopreserved semen is influenced by a range of factors, including storage temperature, cooling rate, chemical composition of the extender, the concentration of cryoprotectant, reactive oxygen species, seminal plasma composition and hygienic control. The choice of cryoprotectant is a vital factor underlying the success of animal semen cryopreservation. In this regard, extensive research has been carried out on various cryoprotectants, such as egg yolk, dimethyl sulfoxide, methanol, ethylene glycol and dimethylacetamide. Recent studies have also described the use of a range of new cryoprotectants for cryopreservation, including compounds of plant origin (soy), amino acids, antifreeze proteins, carbohydrates and cyclodextrins. Moreover, semen cryopreservation and storage require the use of liquid nitrogen or ultralow refrigeration methods for both long- and short-term storage. This review summarizes the general methods used for freezing semen and discusses the use of traditional and newly emerging cryoprotectants (permeable and non-permeable) for the cryopreservation of semen in selected fish and mammalian species.

Combined addition of L-carnitine and L-proline improves cryopreservation of dairy goat semen

Cryopreservation of semen renders artificial insemination easier and cheaper compared to use of fresh semen. However, the cellular oxidative stress, toxicity of cryoprotectants, and osmotic imbalance may lead to a decline in semen quality and fertilization ability during the process of cryopreservation. L-carnitine and L-proline have been demonstrated to possess effective antioxidant properties in cryopreservation, with the latter also exhibiting excellent permeability and thus being utilized as a permeable cryoprotectant in the field. The aim of this study was to investigate the effects of LC and LP on cryopreservation of semen of dairy goats. After thawing, sperm motility, membrane integrity, and acrosome integrity rate of cryopreserved semen treated with LC (50 mM) were significantly higher compared to the untreated control samples. Based on this premise, we conducted experiments to assess the cryoprotective efficacy of different concentrations of LP. The findings demonstrated that the inclusion of 50 mM LP resulted in improved sperm motility compared to other concentrations. Furthermore, the levels of damaging reactive oxygen species and the malonyldialdehyde marker for oxidative stress were significantly lower in goat semen treated with these concentrations of LC and LP compared to semen exposed to other treatments. Semen treated with LC and LP also exhibited good fertilization ability during both in vitro fertilization and artificial insemination. Thus, LC (50 mM) and LP (50 mM) improve cryoprotection of dairy goat sperm which suggests that addition of these compounds will be highly beneficial to the development of dairy goat breeding.

Lyoprotectant Formulation and Optimization of the J-Aggregates Astaxanthin/BSA/Chitosan Nanosuspension

Astaxanthin is a carotenoid with excellent antioxidant activity. However, this small lipid-soluble molecule is insoluble in water and has low stability. Although this situation can be improved when astaxanthin is prepared as a nanosuspension, the aqueous form is still not as convenient and safe as the dry powder form for storage, transport, and use. The lyophilization process provides better protection for thermosensitive materials, but this leads to collapse and agglomeration between nanoparticles. To improve this situation, appropriate lyophilization protectants are needed to offer support between the nanoparticles, such as sugars, amino acids, and hydroxy alcohols. The purpose of this work is to screen lyophilization protectants by single-factor experiments and response surface optimization experiments and then explore the optimal ratio of compound lyophilization protectants, and finally, make excellent astaxanthin/BSA/chitosan nanosuspension (ABC-NPs) lyophilized powder. The work shows that the optimal ratio of the compounding lyophilization protectant is 0.46% oligomeric mannose, 0.44% maltose, and 0.05% sorbitol (w/v). The ABC-NPs lyophilized powder prepared under the above conditions had a re-soluble particle size of 472 nm, with a ratio of 1.32 to the particle size of the sample before lyophilization. The lyophilized powder was all in the form of a pink layer. The sample was fluffy and dissolved entirely within 10 s by shaking with water. Consequently, it is expected to solve the problem of inconvenient storage and transportation of aqueous drugs and to expand the application of nanomedicine powders and tablets.

L-Proline: An Effective Agent for Frozen and Post-thawed Donkey Semen Storage

The aim of this study was to evaluate the effects of L-proline on the extender quality of frozen and post-thawed jackass semen. Jackass (n = 6) semen samples were collected and cryopreserved in gradient concentrations (0-80 mM) of L-proline in extenders; post-thawed semen samples were cultured in L-proline medium for 10 hours at 37°C. For cryopreservation experiment I, the motile parameters, mitochondrial membrane potential (MMP), and plasma membrane, acrosome, and chromatin structure integrities of post-thawed semen were assessed. For culture experiment II, additional ROS contents were analyzed after incubation. For the fertility trial, jennies (n = 135) were divided into group I (30 mM L-proline in cryopreservation extender), group II (40 mM L-proline in culture medium), and the control. Pregnancy was diagnosed using an ultrasound scanner 30 days after ovulation. The results of experiment I showed that, motile parameters and acrosome and chromatin structure integrities of groups I and 40 mM were significantly higher than the control (P < .05). MMP of group I was significantly higher than the control and 40 mM groups (P < .05). In experiment II, after 4 hours of incubation, motile parameters, MMP, and DNA integrity in group II were significantly higher than the control (P < .05). Additionally, 40 and 80 mM L-proline in culture medium significantly reduced ROS accumulation after 4 and 10 hours of incubation (P < .05). Pregnancy rates of the control and groups I and II were 28.85%, 40%, and 36.84%, respectively. In conclusion, the extenders containing 30 to 40 mM L-proline improved both qualities of frozen and post-thawed semen, and it will be a beneficial agent for donkey frozen spermatozoa or post-thawed semen storage.

Evaluation of pentoxifylline and Basal Medium Eagle supplemented to diluent on cryopreserved goat spermatozoa

This study investigated the effect of pentoxifylline (PTX) and Basal Medium Eagle (BME) on frozen-thawed goat spermatozoa. Immediately after initial examination of ejaculated semen, samples were pooled and reexamined for quality. Then, samples were divided into eight equal aliquots and diluted with a basic tris-extender containing PTX (3, 6, 9 mM) and BME (5 mM) to reach a final concentration of 25 × 10⁹ and frozen. After 24 hr, the samples were individually thawed at 37°C for 30 s and evaluated for different characteristics. Obtained post-thaw results from Computer-Assisted Sperm Analysis indicate using of 3 and 6 mM PTX led significantly to an improvement in total motility, progressive motility and velocity characteristics of spermatozoa, except the beat/cross frequency (BCF) which indicated statistically no differences (p > .05) among control and treatments. Diluents prepared with BME (5 mM) and PTX alone (3 and 6 mM) improved significantly the membrane integrity-functionality, acrosome integrity and also hyaluronidase activity. Regarding recovery rate, the results showed significantly (p < .05) higher values for diluents containing 3 and 6 mM PTX compared to other groups. Malondialdehyde concentration exhibited also a significant difference (p < .05) in diluents supplemented with 5 mM BME, 3, 6 and 9 mM PTX, and mixture of 3 mM PTX and 5 mM BME which illustrate a similarity for active mitochondria, apoptotic-like and dead spermatozoa. Finally, the ratio of sperm chromatin dispersion stained spermatozoa presented significant differences (p < .05) among treatments in which the diluents added PTX alone demonstrated significantly lower values than control and extenders containing the mixtures of BME and PTX. In conclusion, the observation in this study indicates using of 3 and 6 mM PTX and BME alone may improve significantly (p < .05) the quality of cryopreserved goat spermatozoa.

Seminal plasma amino acid profile in different breeds of chicken: Role of seminal plasma on sperm cryoresistance

Seminal plasma is a key biological fluid that modulates sperm function in the reproduction process. However, its role in sperm biotechnologies is scarce in poultry. The aims of the present study were to study the amino acids profile and total proteins of seminal plasma in 12 Spanish chicken breeds and to investigate the role of seminal plasma on cryoresistance of rooster sperm. To investigate the role of seminal plasma on cryoresistance, diluted pooled semen samples were cryopreserved in the presence and absence of seminal plasma. Glutamic acid was the most abundant free amino acid in seminal plasma, followed by alanine, serine, valine, and glycine. There was an influence of breed (P<0.05) on the percentage of viable sperm after freezing-thawing of samples with seminal plasma. Cluster analysis revealed that White Prat, Black Castellana, Blue Andaluza, Quail Castellana, and Red-Barred Vasca returned the best freezing-thawing response (good freezers). There was a positive correlation between seminal plasma concentrations of valine, isoleucine lysine, leucine and post thaw viability. The evaluation of fertilization capacity of frozen-thawed semen from the breeds White Prat ('good freezer') and Black-Red Andaluza ('bad freezer') showed that good freezer had higher fertility (20/68, 29.4%) compared to bad freezer breed (14/76, 18.4%), even if the difference was not significant (P = 0.08). The TUNEL assay revealed that freezing/thawing procedures in presence of seminal plasma provoked higher DNA fragmentation in most of the breeds, with a positive correlation between seminal alanine, valine, isoleucine, methionine, leucine, tyrosine, phenylalanine concentrations and DNA integrity. DNA fragmentation was lower in absence of seminal plasma and the breed effect on sperm viability was highly reduced. It is concluded that specific seminal plasma amino acids were associated with post-thaw percentage of viable sperm and DNA integrity. The removal of seminal plasma decreases the variability of the results and DNA fragmentation damages.

Carnosine and Histidine Supplementation Blunt Lead-Induced Reproductive Toxicity through Antioxidative and Mitochondria-Dependent Mechanisms

Lead (Pb)-induced reproductive toxicity is a well-characterized adverse effect associated with this heavy metal. It has been found that Pb exposure is associated with altered spermatogenesis, increased testicular degeneration, and pathological sperm alterations. On the other hand, it has been reported that Pb-induced reproductive toxicity is associated with increased reactive oxygen species (ROS) formation and diminished antioxidant capacity in the reproductive system. Hence, administration of antioxidants as protective agents might be of value against Pb-induced reproductive toxicity. This study was designed to investigate whether carnosine (CAR) and histidine (HIS) supplementation would mitigate the Pb-induced reproductive toxicity in male rats. Animals received Pb (20 mg/kg/day, oral, 14 consecutive days) alone or in combination with CAR (250 and 500 mg/kg/day, oral, 14 consecutive days) or HIS (250 and 500 mg/kg/day, oral, 14 consecutive days). Pb toxicity was evident in the reproductive system by a significant increase in tissue markers of oxidative stress along with severe histopathological changes, seminal tubule damage, tubular desquamation, low spermatogenesis index, poor sperm parameters, and impaired sperm mitochondrial function. It was found that CAR and HIS supplementation blunted the Pb-induced oxidative stress and mitochondrial dysfunction in the rat reproductive system. Thereby, antioxidative and mitochondria-protective properties serve as primary mechanisms for CAR and HIS against Pb-induced reproductive toxicity.

Role of amino acids as additives on sperm motility, plasma membrane integrity and lipid peroxidation levels at pre-freeze and post-thawed ram semen

The possibility of including amino acids for cryopreservation of ram semen to improve the quality of frozen semen was explored in this study in sheep model. 24 samples were collected in triplicate from 8 rams of 2-3 year old Bannur cross bred rams maintained at the Institute Experimental Livestock Unit. Semen was diluted in tris-egg yolk glycerol diluent and made into 7 aliquots as follows: aliquot 1 served as control, "l-alanine" was added at 100 and 135mM in the aliquots 2 and 3, "l-glutamine" was added at 20 and 25mM in the aliquots 4 and 5 and "l-proline" was added at 25 and 50mM in the aliquots 6 and 7, respectively. Diluted semen was filled in 0.25ml French straws and frozen in LN2. Inclusion of "l-proline" and "l-glutamine" in the diluent increased the percent live sperm (P<0.001), total motility (P<0.05) and maintained higher functional membrane and acrosomal integrity (P<0.001) by decreasing lipid peroxidation (P<0.001) compared to the control group. In contrast, "l-alanine" decreased the percentage of total motility, fast progressive spermatozoa and increased (P<0.01) the percentage of immotile spermatozoa. It can be concluded that 20mM "l-glutamine" and 25mM "l-proline" can be used as semen additive to freeze ram semen as they prevented cryoinjuries to sperm and improved the pre-freeze and post-thaw semen characteristics.

Ice-induced partial unfolding and aggregation of an integral membrane protein

Although the deleterious effects of ice on water-soluble proteins are well established, little is known about the freeze stability of membrane proteins. Here we explore this issue through a combined kinetic and spectroscopic approach using micellar-purified plasma membrane calcium pump as a model. The ATPase activity of this protein significantly diminished after freezing using a slow-cooling procedure, with the decrease in the activity being an exponential function of the storage time at 253K, with t(½)=3.9±0.6h. On the contrary, no significant changes on enzyme activity were detected when a fast cooling procedure was performed. Regardless of the cooling rate, successive freeze-thaw cycles produced an exponential decrease in the Ca(2+)-ATPase activity, with the number of cycles at which the activity was reduced to half being 9.2±0.3 (fast cooling) and 3.7±0.2 (slow cooling). PAGE analysis showed that neither degradation nor formation of SDS-stable aggregates of the protein takes place during protein inactivation. Instead, the inactivation process was found to be associated with the irreversible partial unfolding of the polypeptide chain, as assessed by Trp fluorescence, far UV circular dichroism, and 1-anilino-naphtalene-8-sulfonate binding. This inactive protein undergoes, in a later stage, a further irreversible transformation leading to large aggregates.

Amino acids as cryoprotectants for liposomal delivery systems

Liposomes provide an efficient delivery system for solubilisation and delivery of both small and macro molecules. However, they suffer from the disadvantage of instability when stored as aqueous dispersions. Cryoprotection of the liposomal systems provides an effective approach to overcome poor stability whilst maintaining formulation characteristics, although, the formulation of a freeze-dried product requires the consideration of not only the selection of an appropriate cryoprotectant, but also needs careful consideration of the processing parameters including pre-freezing conditions, primary and secondary drying protocols along with optimisation of cryoprotectant concentration. This current work investigates the application of amino acids as potential cryoprotectants for the stabilisation of liposomes, and results indicate that amino acids show biphasic nature of stabilisation with 4 mol of cryoprotectant per mole of the lipid exhibiting optimum cryoprotection. The investigations of process parameters showed that the pre-freezing temperatures below the glass transition of the amino acids followed by drying for over 6h resulted in stable formulations. Studies investigating the efficiency of drug retention showed that the cryoprotection offered by lysine was similar to that shown by trehalose, suggesting that amino acids act as effective stabilizers. ESEM analysis was carried out to monitor morphology of the rehydrated liposomes.

Beta2-agonist administration increases sarcoplasmic reticulum Ca2+-ATPase activity in aged rat skeletal muscle

Aging is associated with a slowing of skeletal muscle contractile properties, including a decreased rate of relaxation. In rats, the age-related decrease in the maximal rate of relaxation is reversed after 4-wk administration with the beta2-adrenoceptor agonist (beta2-agonist) fenoterol. Given the critical role of the sarcoplasmic reticulum (SR) in regulating intracellular Ca2+ transients and ultimately the time course of muscle contraction and relaxation, we tested the hypothesis that the mechanisms of action of fenoterol are mediated by alterations in SR proteins. Sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) kinetic properties were assessed in muscle homogenates and enriched SR membranes isolated from the red (RG) and white (WG) portions of the gastrocnemius muscle in adult (16 mo) and aged (28 mo) F344 rats that had been administered fenoterol for 4 wk (1.4 mg/kg/day ip, in saline) or vehicle only. Aging was associated with a 29% decrease in the maximal activity (Vmax) of SERCA in the RG but not in the WG muscles. Fenoterol treatment increased the Vmax of SERCA and SERCA1 protein levels in RG and WG. In the RG, fenoterol administration reversed an age-related selective nitration of the SERCA2a isoform. Our findings demonstrate that the mechanisms underlying age-related changes in contractile properties are fiber type dependent, whereas the effects of fenoterol administration are independent of age and fiber type.

Glycogen determination using periodic acid-schiff: artifact of muscle preparation

PURPOSE

It is common practice for the staining of muscle glycogen with periodic acid-Schiff (PAS) to thaw and dry muscle sections before staining. The goal is to investigate whether this thawing step results in a systematic error that is independent of muscle fiber type and muscle physiological state.

METHODS

Muscle samples from six fasted male subjects were obtained before or after 3 min of high-intensity cycling. Each sample was sectioned; some sections were assessed for muscle fiber composition, and others were either thawed for 20 min or kept frozen before being PAS-stained for glycogen. The response to a 20-min freeze-thaw cycle was also assessed using rested and exercised rats as our experimental model, and the changes in glycogen were measured enzymatically.

RESULTS

The inclusion of a 20-min thawing step resulted in a significant reduction (P < 0.05) in the weighted average of the optical density of PAS (ODPAS) staining in both the nonexercised (15 +/- 1.4%) and exercised human muscles (15 +/- 1.3%), with the absolute extent being greater in the nonexercised muscle samples (P < 0.05). Moreover, the observed decrease in ODPAS was greatest in Type IIa fibers for both the nonexercised (P < 0.05) and exercised (P < 0.05) muscle samples. The findings in rats suggest that the muscle damage associated with freeze-thawing is responsible for this stimulation of glycogenolysis.

CONCLUSION

For the quantitative histochemical measurement of glycogen content in skeletal muscle, the common practice of thawing unfixed muscle sections before PAS staining should be abandoned because this causes glycogen breakdown, the extent of which varies across muscle fiber types and prior exercise history.

Effects of glutamine on post-thaw motility of stallion spermatozoa: an approach of the mechanism of action at spermatozoa level

The cryoprotective effect of l-glutamine and an approach of its mechanism of action, in preserving motility of stallion spermatozoa during the freezing-thawing process, were studied. In Experiment 1, thirty-six ejaculates were collected from six stallions (two good, two middle, and two of poor sperm freezability) and were diluted with 10 different freezing media derived from INRA 82 medium supplemented with 20 mM HEPES and 2% (v/v) centrifuged egg yolk (BM). After thawing, sperm motility was evaluated by a computer-assisted semen motility analyser. The effects of glutamine and glycerol at different concentrations on post-thaw sperm motility were studied. A possible interaction between medium and semen freezability was investigated. Only the 50 mM glutamine + 2.5% glycerol medium significantly improved sperm motility compared to classical freezing medium (2.5% glycerol). The presence of glutamine at 50 mM was not sufficient to offset the need to use glycerol in the freezing extender. The use of glutamine at a higher concentration >100 mM in the presence of 2.5% of glycerol was toxic. Reducing the glycerol proportion from 2.5% to 2 or 1.5% in the presence of glutamine at 50, 75, and 100 mM had no influence on post-thaw motility of semen of middle and good freezability. Moreover, the substitution of 2.5% glycerol by 50 mM glutamine in BM, did not significantly change the post-thaw motility of semen of good freezability. In Experiment 2, 3H-glutamine and 3H-glycerol were used to study the kinetics of penetration of glutamine and glycerol in sperm cells. The radioactivity of each radio-labelled semen pellet was measured at different times (0, 15, 30, 60, 90, 120 min), by using a Packard tri-carb 4530 apparatus. The percentages of incorporated radioactivity (%IRA) in semen pellets were calculated at different times. The %IRA of 3H-glycerol in semen pellets were significantly higher than the %IRA of 3H-glutamine. The %IRA of 3H-glycerol in semen pellets increased greatly from time 0 to 60 min, and then it is stabilized from 60 to 120 min. In contrast, the %IRA of 3H-glutamine in semen pellets increased slightly from 0 to 60 min, then it stabilized until 120 min. These experiments demonstrate that glutamine has a synergistic cryoprotective effect with glycerol on cryopreservation of stallion spermatozoa, and suggest that glutamine acts at the extra-cellular level, independently of glycerol.

Skeletal muscle sarcoplasmic reticulum glycogen status influences Ca2+ uptake supported by endogenously synthesized ATP

The purpose of this investigation was to determine whether there is a link between sarcoplasmic reticulum (SR) glycogen status and SR Ca2+ handling. In this investigation, skeletal muscle SR was purified from female Sprague-Dawley rats (200-250 g). Glycogen was extracted from the SR purified from one hindlimb, whereas the SR purified from the contralateral limb served as control. Before removal of the tissue, the animals were anesthetized with an intraperitoneal injection of ketamine (80 mg/kg) and xylazine (10 mg/kg). Both alpha-amylase treatment (AM) and removal of EDTA from the homogenization and storage buffers reduced the amount of glycogen associated with the SR (P < 0.05). AM treatment reduced the glycogen phosphorylase content of SR (P < 0.05). In contrast, creatine kinase (CK) and pyruvate kinase (PK) contents were increased after both glycogen extraction protocols (P < 0.05). Under exogenous ATP conditions, both AM and EDTA-free (EF) treatments resulted in an increase in Ca2+-stimulated ATPase activity when normalized to sarco(endo)plasmic reticulum calcium-ATPase (SERCA) content (P < 0.05). CK and PK-supported SR Ca2+ uptake was decreased (P < 0.05) in the AM group when normalized to SERCA and CK or SERCA and PK content, respectively. AM was more effective than the EF for extracting glycogen associated with purified SR. Glycogen extraction alters the yield of purified SR proteins and must be taken into account when investigating SR calcium handling. Removal of glycogen from purified SR causes a change in Ca2+-handling properties as measured by ATPase and uptake activities.

Mechanisms underlying increases in SR Ca2+-ATPase activity after exercise in rat skeletal muscle

Prolonged exercise followed by a brief period of reduced activity has been shown to result in an overshoot in maximal sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity [maximal velocity (V(max))] in rat locomoter muscles (Ferrington DA, Reijneveld JC, Bär PR, and Bigelow DJ. Biochim Biophys Acta 1279: 203-213, 1996). To investigate the functional significance and underlying mechanisms for the increase in V(max), we analyzed Ca(2+)-ATPase activity and Ca(2+) uptake in SR vesicles from the fast rat gastrocnemius muscles after prolonged running (RUN) and after prolonged running plus 45 min of low-intensity activity (RUN+) or no activity (REC45) and compared them with controls (Con). Although no differences were observed between RUN and Con, both V(max) and Ca(2+) uptake were higher (P < 0.05) by 43 and 63%, respectively, in RUN+ and by 35 and 34%, respectively, in REC45. The increase in V(max) was accompanied by increases (P < 0.05) in the phosphorylated enzyme intermediate measured by [gamma-(32)P]ATP. No differences between groups for each condition were found for the fluorescent probes FITC and (N-cyclohexyl-N(1)-dimethylamino-alpha-naphthyl)carbodiimide, competitive inhibitors of the nucleotide-binding and Ca(2+)-binding sites on the enzyme, respectively. Similarly, no differences for the Ca(2+)-ATPase were observed between groups in nitrotyrosine and phosphoserine residues, a measure of nitrosylation and phosphorylation states, respectively. Western blots indicated no changes in relative isoform content of sarcoendoplasmic reticulum (SERCA)1 and SERCA2a. It is concluded that the increase in V(max) of the Ca(2+)-ATPase observed in recovery is not the result of changes in enzyme nitroslyation or phosphorylation, changes in ATP and Ca(2+)-binding affinity, or changes in protein content of the Ca(2+)-ATPase.

Ischemia-induced structural change in SR Ca2+-ATPase is associated with reduced enzyme activity in rat muscle

In this study, we employed an in vivo model of prolonged ischemia in rat skeletal muscle to investigate the hypothesis that structural modifications to the sarcoplasmic reticulum (SR) Ca2+-ATPase can explain the alterations in Ca2+-ATPase activity that occur with ischemia. To induce total ischemia, a tourniquet was placed around the upper hindlimb in 27 female Sprague-Dawley rats weighing 256 +/- 6.7 g (mean +/- SE) and was inflated to 350 mmHg for 4 h. The contralateral limb served as control (C) to the ischemic limb (I), and the limbs of animals killed immediately after anesthetization served as a double control (CC). Mixed gastrocnemius and tibialis anterior muscles were sampled and used for SR vesicle preparation. Maximal Ca2+-ATPase activity (micromol x g protein(-1) x min(-1)) of C (15,802 +/- 1,246) and I (11,609 +/- 1,029) was 90 and 73% (P < 0.05) of CC (17,562 +/- 1,682), respectively. No differences were found between groups in either the Hill coefficient or the free Ca2+ at half-maximal activity. The fluorescent probes, FITC and N-cyclohexyl-N'-(dimethylamino-alpha-naphthyl) carbodiimide, used to assess structural alterations in the regions of the ATP binding site and the Ca2+ binding sites of the Ca2+-ATPase, respectively, indicated a 26% reduction (P < 0.05) in FITC binding capacity (absolute units) in I (0.22 +/- 0.01) compared with CC (0.29 +/- 0.02) and C (0.29 +/- 0.03). Our results suggest that the reduction in maximal SR Ca2+-ATPase activity in SR vesicles with ischemia is related to structural modification in the region of the nucleotide binding domain by mechanisms that are as yet unclear.

Effects of 4-h ischemia and 1-h reperfusion on rat muscle sarcoplasmic reticulum function

To investigate the hypothesis that ischemia and reperfusion would impair sarcoplasmic reticulum (SR) Ca(2+) regulation in skeletal muscle, Sprague-Dawley rats (n = 20) weighing 290 +/- 3.5 g were randomly assigned to either a control control (CC) group, in which only the effects of anesthetization were studied, or to a group in which the muscles in one hindlimb were made ischemic for 4 h and allowed to recover for 1 h (I). The nonischemic, contralateral muscles served as control (C). Measurements of Ca(2+)-ATPase properties in homogenates and SR vesicles, in mixed gastrocnemius and tibialis anterior muscles, indicated no differences between groups on maximal activity, the Hill coefficient, and Ca(50), defined as the Ca(2+) concentration needed to elicit 50% of maximal activity. In homogenates, Ca(2+) uptake was lower (P < 0.05) by 20-25%, measured at 0.5 and 1.0 microM of free Ca(2+) ([Ca(2+)](f)) in C compared with CC. In SR vesicles, Ca(2+) uptake was lower (P < 0.05) by 30-38% in I compared with CC at [Ca(2+)](f) between 0.5 and 1.5 microM. Silver nitrate induced Ca(2+) release, assessed during both the initial, early rapid (phase 1), and slower, prolonged late (phase 2) phases, in homogenates and SR vesicles, indicated a higher (P < 0.05) release only in phase 1 in SR vesicles in I compared with CC. These results indicate that the alterations in SR Ca(2+) regulation, previously observed after prolonged ischemia by our group, are reversed within 1 h of reperfusion. However, the lower Ca(2+) uptake observed in long-term, nonischemic homogenates suggests that altered regulation may occur in the absence of ischemia.

Effects of glutamine, proline, histidine and betaine on post-thaw motility of stallion spermatozoa

The supplementation of the freezing diluent with 3 amino acids (glutamine, proline and histidine) and 1 amino acid-related compound (betaine) in preserving stallion spermatozoa diluted in INRA82 extender containing 2.5% (v/v) glycerol and 2% (v/v) egg yolk (control extender) during freezing and thawing was studied at 0, 40, 80, 120 and 160 mM in 20 split ejaculates (10 stallions x 2 ejaculates; Experiment 1). Glutamine and proline were studied at 0, 10, 20, 30, 40, 50, 60, 70 and 80 mM in 20 split ejaculates (10 stallions x 2 ejaculates; Experiment 2). In each experiment, spermatozoa were evaluated after thawing by computer automated sperm analyzer. The percentage of motile spermatozoa (faster than 30 microns/sec) was assessed. In addition, the velocity of the average path (VAP), the straight line velocity (VSL), the curvilinear velocity (VCL) and the amplitude of the lateral head displacement (ALH) were also measured. In Experiment 1, only glutamine (40 mM) significantly improved sperm motility (56.0% +/- 3.0 vs 49.7% +/- 1.6; P < 0.05) compared with the control extender, while velocities were unaffected at concentrations of 40 to 120 mM. However, at 160 mM, a significant decrease in motility and velocity was observed for all amino acids. In Experiment 2, motility in glutamine (range 41.1% +/- 3.8%; 42.4% +/- 3.6) and proline (43.0% +/- 3.7; 45.6% +/- 3.8) extenders compared with the control (34.7% +/- 1.6) was improved significantly (P < 0.05). Sperm velocity was improved at concentrations higher than 40 mM glutamine and 50 mM proline.

Improvement of motility of post-thaw Poitou jackass sperm using glutamine

The relative effectiveness of L-glutamine in preserving motility and movement characteristics of Poitou jackass spermatozoa diluted at 60 x 10(6) sperm/ml in INRA 82 medium modified by 4 % (v/v) glycerol and 2 % (v/v) quail's egg yolk during the cooling and freezing-thawing process was studied. After cooling to 4 degrees C, glutamine at 80, 120 or 240 mM did not improve the percentages of motile and progressively undulating spermatozoa or the movement characteristics (VCL = curvilinear velocity, VSL = straight line velocity, VAP = velocity of the average path, LIN = VSL/VCL x 100, ALH = amplitude of the lateral head displacement, BCF = beat cross frequency) assessed by the automated analyzer ATSM. However, after the FT process, 80 mM glutamine significantly improved motility, the percentage of progressively undulating spermatozoa and all the movement characteristics analyzed. The presence of glutamine at 80 mM in a glycerol-FT medium thus improves the motility of Poitou jackass spermatozoa during the freezing-thawing process. The presence of glutamine at 80 mM was not sufficient to offset the need to use glycerol in the freezing-thawing medium. This could indicate that glutamine has a mechanism of cryoprotection for Poitou jackass spermatozoa that is independant of glycerol.

Effects of prolonged low frequency stimulation on skeletal muscle sarcoplasmic reticulum

The role of prolonged electrical stimulation on sarcoplasmic reticulum (SR) Ca2+ sequestration measured in vitro and muscle energy status in fast white and red skeletal muscle was investigated. Fatigue was induced by 90 min intermittent 10-Hz stimulation of rat gastrocnemius muscle, which led to reductions (p < 0.05) in ATP, creatine phosphate, and glycogen of 16, 55, and 49%, respectively, compared with non-stimulated muscle. Stimulation also resulted in increases (p < 0.05) in muscle lactate, creatine, Pi, total ADP, total AMP, IMP, and inosine. Calculated free ADP (ADPf) and free AMP (AMPf) were elevated 3- and 15-fold, respectively. No differences were found in the metabolic response between tissues obtained from the white (WG) and red (RG) regions of the gastrocnemius. No significant reductions is SR Ca2+ ATPase activity were observed in homogenate (HOM) or a crude SR fraction (CM) from WG or RG muscle following exercise. Maximum Ca2+ uptake in HOM and CM preparations was similar in control (C) and stimulated (St) muscles. However, Ca2+ uptake at 400 nM free Ca2+ was significantly reduced in CM from RG (0.108 +/- 0.04 to 0.076 +/- 0.02 mumol.mg-1 protein.min-1 in RG - C and RG - St, respectively). Collectively, these data suggest that reductions in muscle energy status are dissociated from changes in SR Ca2+ ATPase activity in vitro but are related to Ca2+ uptake at physiological free [Ca2+ bd in fractionated SR from highly oxidative muscle. Dissociation of SR Ca2+ ATPase activity from Ca2+ uptake may reflect differences in the mechanisms evaluated by these techniques.

Protective effects of amino acids against freeze-thaw damage in mammalian cells

Amino acids were tested for their effectiveness as cryoprotectants. From the results of this study, the mean fractional area loss of amino acid residues upon incorporation in globular proteins, a measure of hydrophobicity, is generally inversely proportional to the freeze-thaw protection by these free amino acids. However, the pattern of protection ("fingerprint") of cells by various amino acids is different from that of the enzymes liver alcohol dehydrogenase and calcium ATPase of the sarcoplasmic reticulum. Furthermore, unlike the case with these enzymes, for cells glutamine is the best cryoprotective agent of the amino acids tested.