Permeation kinetics of glycerol and dimethyl sulfoxide in Novikoff hepatoma ascites cells

Sperm collection and storage for the sustainable management of amphibian biodiversity

Current rates of biodiversity loss pose an unprecedented challenge to the conservation community, particularly with amphibians and freshwater fish as the most threatened vertebrates. An increasing number of environmental challenges, including habitat loss, pathogens, and global warming, demand a global response toward the sustainable management of ecosystems and their biodiversity. Conservation Breeding Programs (CBPs) are needed for the sustainable management of amphibian species threatened with extinction. CBPs support species survival while increasing public awareness and political influence. Current CBPs only cater for 10% of the almost 500 amphibian species in need. However, the use of sperm storage to increase efficiency and reliability, along with an increased number of CBPs, offer the potential to significantly reduce species loss. The establishment and refinement of techniques over the last two decades, for the collection and storage of amphibian spermatozoa, gives confidence for their use in CBPs and other biotechnical applications. Cryopreserved spermatozoa has produced breeding pairs of frogs and salamanders and the stage is set for Lifecycle Proof of Concept Programs that use cryopreserved sperm in CBPs along with repopulation, supplementation, and translocation programs. The application of cryopreserved sperm in CBPs, is complimentary to but separate from archival gene banking and general cell and tissue storage. However, where appropriate amphibian sperm banking should be integrated into other global biobanking projects, especially those for fish, and those that include the use of cryopreserved material for genomics and other research. Research over a broader range of amphibian species, and more uniformity in experimental methodology, is needed to inform both theory and application. Genomics is revolutionising our understanding of biological processes and increasingly guiding species conservation through the identification of evolutionary significant units as the conservation focus, and through revealing the intimate relationship between evolutionary history and sperm physiology that ultimately affects the amenability of sperm to refrigerated or frozen storage. In the present review we provide a nascent phylogenetic framework for integration with other research lines to further the potential of amphibian sperm banking.

Communication: Contrasting effects of glycerol and DMSO on lipid membrane surface hydration dynamics and forces

Glycerol and dimethyl sulfoxide (DMSO) are commonly used cryoprotectants in cellular systems, but due to the challenges of measuring the properties of surface-bound solvent, fundamental questions remain regarding the concentration, interactions, and conformation of these solutes at lipid membrane surfaces. We measured the surface water diffusivity at gel-phase dipalmitoylphosphatidylcholine (DPPC) bilayer surfaces in aqueous solutions containing ≤7.5 mol. % of DMSO or glycerol using Overhauser dynamic nuclear polarization. We found that glycerol similarly affects the diffusivity of water near the bilayer surface and that in the bulk solution (within 20%), while DMSO substantially increases the diffusivity of surface water relative to bulk water. We compare these measurements of water dynamics with those of equilibrium forces between DPPC bilayers in the same solvent mixtures. DMSO greatly decreases the range and magnitude of the repulsive forces between the bilayers, whereas glycerol increases it. We propose that the differences in hydrogen bonding capability of the two solutes leads DMSO to dehydrate the lipid head groups, while glycerol affects surface hydration only as much as it affects the bulk water properties. The results suggest that the mechanism of the two most common cryoprotectants must be fundamentally different: in the case of DMSO by decoupling the solvent from the lipid surface, and in the case of glycerol by altering the hydrogen bond structure and intermolecular cohesion of the global solvent, as manifested by increased solvent viscosity.

Cryopreservation of postnatal rat retinal ganglion cells: persistence of voltage- and ligand-gated ionic currents

Established methods for cryopreservation of living cells were modified for freeze-storage of postnatal retinal ganglion cells from rat. Retinal cell suspensions containing fluorescently labeled ganglion cells were frozen after addition of 8% dimethyl sulfoxide and stored at -80 degrees C for up to 66 days. Viability of identified retinal ganglion cells was assessed by their ability to take up and cleave fluorescein diacetate to fluorescein. No significant difference was found in the number of living retinal ganglion cells when cells obtained from the same dissociation were counted before and after freezing (6.65 +/- 2.37 x 10(4) vs 7.05 +/- 3.67 x 10(4) retinal ganglion cells per ml, respectively; mean +/- S.D., n = 4). In culture following cryopreservation, the cells appeared morphologically normal, and developed neurites and growth cones similar to their freshly dissociated counterparts. Since very little is known about the electrophysiology and membrane properties of neurons after cryopreservation, we used the whole-cell configuration of the patch-clamp technique to study voltage- and ligand-gated conductances in cryopreserved retinal ganglion cells. The cryopreserved retinal ganglion cells studied under current-clamp maintained resting potentials of -60.9 +/- 6.6 mV (n = 10) and upon depolarization fired action potentials. During voltage-clamp in the whole-cell mode, depolarizing voltage steps activated Na(+)-(INa), Ca(2+)-(ICa), and K(+)-currents in all cells tested (n = 122). INa could be reversibly blocked by 1 microM tetrodotoxin added to the external solution. ICa was blocked by external 250 microM Cd2+ or 3 mM Co2+. In some cells, ICa consisted of both a transient and prolonged component. The outward K(+)-current consisted of Ca(2+)-dependent and -independent components. The Ca(2+)-insensitive portion of the K+ outward current was separated into four distinct components based upon pharmacological sensitivity and biophysical properties. In many cells, a rapidly inactivating current similar to the A-type K(+)-current (IA) observed in freshly cultured retinal ganglion cells was isolated by its greater sensitivity to 4-aminopyridine (5 mM) than to tetraethylammonium (20 mM). A tetraethylammonium-sensitive current with a more prolonged time course reminiscent of IK, the delayed rectifier, was also found. When the 4-aminopyridine- and tetraethylammonium-insensitive portions of the outward current were further analysed with voltage protocols, an additional slowly decaying potassium current became apparent. The inhibitory amino acids, GABA (20 microM) and glycine (100 microM), activated chloride-selective currents that were selectively blocked by bicuculline methiodide (10 microM) and strychnine (5 microM), respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Tolerance of human corneal endothelium to glycerol

As an initial step in the development of a method for corneal cryopreservation by vitrification, we attempted to establish the maximum concentration of glycerol to which human corneal endothelium could be exposed at 4 degrees C for 15 min without damage. Damage was defined as an increase in mean endothelial cell size or the inability to maintain corneal thickness for 1 week after exposure to glycerol. Using a system for long-term corneal perfusion, we perfused 24 paired human corneas with glycerol at 4 degrees C. The concentration of glycerol increased at a rate of 20% (w/v) (2.2 M) per hour until the desired maximum concentration was reached for that cornea, stabilized for 15 min, and then decreased at the same rate. The corneas were then perfused at 37 degrees C with Dulbecco's medium at a rate of 5 microliters/min under 18 mm Hg intracameral pressure for 7 days with daily measurements of corneal thickness. Endothelial morphology was examined by specular microscopy and by scanning electron microscopy. After 7 days of perfusion at 37 degrees C, there was a statistically significant direct relationship between the maximum concentration of glycerol to which the experimental eyes had been exposed and the increase in mean endothelial cell size. The mean endothelial cell size increased in corneas exposed to glycerol concentrations of 40, 50, and 60% (w/v), but did not differ significantly from baseline measurements in the corneas exposed to 30% glycerol or less. Thus, there was no detectable damage to human corneas exposed to 30% (w/v) (3.3 M) glycerol in this system. Tolerance of higher concentrations may be achieved by changes in the rates of addition and removal of glycerol or in the composition of the perfusate.

The assessment of endothelial integrity by scanning electron microscopy and fluorescein diacetate staining following treatment with cryoprotective additives

As part of the development of methods of corneal cryostorage for transplantation, a toxicity study was carried out on the rabbit corneal endothelium using four cryoprotective additives (CPA's) 1) dimethyl sulphoxide (Me2SO), 2) propane-1,2-diol (PG), 3) glycerol (GLY), 4) polyvinylpyrrolidone (PVP). A fifth group, based upon a CPA combination of Me2SO and PVP, was used to characterize both the assays, and the response of the endothelial layer to osmotic stress. The effect upon the cell membrane was assessed using scanning electron microscopy (SEM) and fluorescein diacetate with ethidium bromide staining (FDA/EB). Two sampling points were used, one immediately after treatment and the other following an incubation period. Calculations were performed to predict the maximum relative volume of cells during CPA exchange. Immediately following serial addition and removal of 2 or 3 mol/L (M) PG or GLY, the cells exhibited adverse morphological changes shown with SEM, and the proportion of intact cells judged by FDA/EB staining was significantly reduced when CPA equilibration was performed at 37 degrees C rather than at 20 degrees C. A 3M Me2SO concentration gave less morphological change than 3M PG or GLY, but even after treatment with 4M Me2SO more than 95% cells were judged intact by FDA/EB staining. PVP at 40% w/v showed minimal damage with both assays, and the fifth experimental group suggested that PVP may protect from injury during hypotonic stress. With all groups, the integrity of the cell layer recovered during incubation, so that for each sample the percentage of intact cells was high. However, although confluency was often restored following incubation, total cell density was usually reduced. The results indicate that serial addition and removal of 3M Me2SO is tolerated by the cornea, whereas PG or GLY cannot be used at 2 or 3M without inducing osmotic damage. There was low toxicity to PVP, and it was an effective osmotic buffer.

A comparative investigation of glycinebetaine and dimethylsulphoxide as liposome cryoprotectants

The release of streptomycin from lecithin liposomes following a freeze-thaw cycle was used to measure the cryoprotective activities of glycinebetaine and dimethylsulphoxide (DMSO). At concentrations between 4 and 8% w/v in the external solution, glycinebetaine was superior to DMSO at freezing rates faster than 50 degrees C min-1. At lower rates their activities were similar, and drug loss ranged between 10 and 20% depending upon freezing rate and cryoprotectant concentration. The pattern of streptomycin loss when the concentrations of cryoprotectants inside and outside the liposome were varied indicated that glycinebetaine, in contrast to DMSO, does not diffuse across the liposome membrane. The activity of glycinebetaine was not impaired by the presence in the membrane of cholesterol or charged lipids.

Cryopreservation of fetal rat brain tissue later used for intracerebral transplantation

Intracerebral grafting of immature brain tissue is now widely used as a tool to study neuronal development and regeneration in the brain and spinal cord. This has stimulated the interest in methods for storage of such tissue before transplantation. In this study a method for cryopreservation of immature rat central nervous tissue is presented and discussed in relation to current cryobiological principles. The method was applied to brain tissue from 16- and 17-day-old fetal rats, including the neocortex, habenula, septum and basal forebrain, cerebellum, and retina. After storage in liquid nitrogen from 6 to 52 days the tissue was grafted into the brain of adult rats. The recipients survived for 23 to 673 days before their brains were processed by current neuroanatomical, histological methods. The presence of graft tissues was recorded and their cellular and connective organization was examined, including their exchange of nerve connections with the host brain. The results obtained were comparable with results from other studies where the same tissues were grafted immediately after removal from the donor, and a study of cryopreservation of developing hippocampal tissue. We conclude that cryopreservation is a reliable method for storage of immature neural tissue later to be used for intracerebral grafting.

Morphological artifacts induced in intracellularly stained neurons by dehydration: circumvention using rapid dimethyl sulfoxide clearing

In order to observe the fine details of intracellularly stained neurons in brain slices the slices must be cleared of opaque matter. This clearing process involves dehydration of the slice, which typically results in significant shrinkage of the cleared tissue. However, how this shrinkage affects neuronal morphology has not been demonstrated to date. In this paper we detail the artifacts induced in the morphology of stained neurons by this clearing process. During dehydration-induced shrinkage of the brain slices, neurons stained with the water-soluble dye, Lucifer yellow, demonstrated a dramatic decrease in size to less than two-thirds of their original dimensions. In contrast neurons stained with the horseradish peroxidase/diaminobenzidine reaction-product did not shrink with the slice; instead the dendrites bent and curled during dehydration with no loss in cell-soma size. We have managed to circumvent these artifacts by using as a clearing agent the solvent dimethyl sulfoxide, which is miscible in both aqueous and organic phases. This solvent will clear tissue slices without inducing the concomitant artifacts caused by tissue shrinkage occurring with the alcohol-dehydration process.

A cryopreservative procedure for storing cultivated and uncultivated amniotic fluid cells in liquid nitrogen

The cryopreservation of cultured and uncultured amniotic fluid cells is of special importance in prenatal diagnosis. The freezing procedure presented gave a cell recovery of about 95% for cultivated human amniotic fluid cells combined with a rapid appearance of mitosis after inoculation.

Permeation of Chinese hamster ovary cells by glycerol: mechanism and kinetics

When monolayer cultures of Chinese hamster ovary cells were exposed to 3H-glycerol ranging in concentration from 0.1 microM to 200 mM, glycerol in flux was found to increase in direct proportion to the extracellular concentration of glycerol. Other experiments indicated that the same relationship existed at concentrations in excess of 1.0 M. Similarly, glycerol efflux was found to vary in direct proportion to the intracellular concentration of glycerol. In neither case could influx or efflux be saturated. Glycerol influx was not affected by depletion of ATP, alkylation by parachloromercuribenzene sulfonic acid, or exposure to persantine. Altering the pH or temperature also had little effect. Attempts at demonstrating countertransport of glycerol were negative. These data indicate that glycerol probably passes through the membrane by a non-mediated process. For cells in monolayer, the kinetics of influx and efflux are biphasic. Similar biphasic kinetics are observed with cells in suspension culture. A close fit to the data may be obtained by adding together two first-order curves. The pair of curves for influx are clearly different from the pair for efflux. The fit provided by the two pairs of first-order functions suggested that glycerol might diffuse into and out of two intracellular compartments. However, the experimental data do not agree with the predicted behavior of a two-compartment system. As a result, the exact nature of the diffusion limiting steps which are described by the first-order equations remains undefined.

Ice crystal growth in skeletal muscle fibres

Ice crystal growth was studied in rapidly frozen skeletal muscle fibres which were treated with cryo-protective additives (glycerol, DMSO, sucrose) or which were untreated. Freeze cleaving and etching was the basic method, with conventional plastic embedding and cryo-ultramicrotomy arred during freezing in all unprotected fibres. Just below the fibre surface the crystals were numerous but small, while deeper in the fibre they were fewer but larger. The deeper within the specimen a fibre was located, the larger, in general, was the crystal size. The crystal volume density was about 55%, irrespective of crystal size. Ice recrystallization was practically absent at the temperature normally used in cryo-sectioning (-70 degrees C). Anti-freeze treatment eliminated crystal growth. If the anti-freeze agents were used in non-toxic concentrations, however, their effect on crystal growth was very limited. 'Dry'-cut, freeze-dried ultra-thin cryosections of protected and unprotected fibres confirmed these observations, while sections obtained by 'wet' cryo-cutting showed no apparent signs of crystal growth. In plastic sections of frozen and thawed fibres a previous occurrence of crystals was only slightly indicated. In interpreting the ultrastructure in 'wet'-cut cryo-sections of unprotected frozen muscle fibres, the distorting effects of ice crystals through mechanical compression and alterations in sectioning conditions, must be taken into consideration. Crystal growth also strongly limits the possibilities of using 'dry'-cut sections of untreated frozen tissue for analytical electron microscopy; only the most superficial parts of the fibres seem to be suitable for microanalysis.

Survival of frozen mycoplasmas

Cooling to -70 C killed a higher percentage of Acholeplasma laidlawii and Mycoplasma mycoides var. capri cells than cooling to -20 C. However, to preserve cell viability for prolonged periods storage at -70 C was much more preferable. The percentage of cells surviving freezing could be increased by increasing the initial cell concentration or by the addition of dimethyl sulfoxide or glycerol as cryoprotective agents. In the presence of 1.5 M of any one of these agents survival rates of up to 100% could be obtained. The optimal cooling rates for maximal survival of A. laidlawii under the experimental conditions tested were 11 C/min for cooling to -20 C and about 15 C/min for cooling to -70 C. Increasing the warming rate during thawing from 0.6 to 67 C/min increased survival by 3 log. Oleic acid enrichment of A. laidlawii membrane lipids, or reduction in the cholesterol content of M. mycoides var. capri membranes, increased the percentage of organisms surviving freezing. Hence, the composition of membrane lipids appears to have a marked influence on the susceptibility of mycoplasmas to freezing injury.

Energy-linked ultrastructural transformations in isolated liver mitochondria and mitoplasts. Preservation of configurations by freeze-cleaving compared to chemical fixation

An investigation was carried out in which microsamples of isolated rat liver mitochondria and freshly prepared mitoplasts in defined energy states were freeze-cleaved. Parallel microsamples were fixed with osmium tetroxide and with glutaraldehyde followed by osmium tetroxide as previously used in this laboratory for the preservation of energy-linked mitochondrial configurations. The details of the orthodox configuration of energized mitochondria and the condensed configuration of de-energized mitochondria, as revealed previously by chemical fixation, are confirmed in this report for nonfixed, freeze-cleaved mitochondria. The precise agreement in preservation of configuration obtained by the physical fixation of rapid freezing and by chemical fixation establishes unequivocally that mitochondria undergo energy-linked ultrastructural transformation between the condensed and the orthodox configurations which are thus natural structural states related to the metabolic activity of the mitochondrion. Configurations observed by freeze-cleaving and by chemical fixation reveal that mitoplasts also undergo a specific and dramatic ultrastructural transformation with the induction of oxidative phosphorylation. The transformation appears to be isovolumetric and therefore is thought to be mediated through energized conformational activity in the surface electron-transport membrane of the mitoplast. Passively swollen, spherical, osmotically active mitoplasts could not be fixed rapidly enough by chemical fixatives as normally used without altering the spherical form. In this special case preservation of configurational form required rapid freezing or chemical fixatives of low osmolar concentration.