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PubMed2006

Geological and geomorphological insights into Antarctic ice sheet evolution.

Technical advances in the study of ice-free parts of Antarctica can provide quantitative records that are useful for constraining and refining models of ice sheet evolution and behaviour. Such records improve our understanding of system trajectory, influence the questions we ask about system stability and help to define the ice-sheet processes that are relevant on different time-scales. Here, we illustrate the contribution of cosmogenic isotope analysis of exposed bedrock surfaces and marine geophysical surveying to the understanding of Antarctic ice sheet evolution on a range of time-scales. In the Dry Valleys of East Antarctica, 3He dating of subglacial flood deposits that are now exposed on mountain summits provide evidence of an expanded and thicker Mid-Miocene ice sheet. The survival of surface boulders for approximately 14Myr, the oldest yet measured, demonstrates exceptionally low rates of subsequent erosion and points to the persistence and stability of the dry polar desert climate since that time. Increasingly, there are constraints on West Antarctic ice sheet fluctuations during Quaternary glacial cycles. In the Sarnoff Mountains of Marie Byrd Land in West Antarctica, 10Be and 26Al cosmogenic isotope analysis of glacial erratics and bedrock reveal steady thinning of the ice sheet from 10400 years ago to the present, probably as a result of grounding line retreat. In the Antarctic Peninsula, offshore analysis reveals an extensive ice sheet at the last glacial maximum. Based on radiocarbon dating, deglaciation began by 17000cal yr BP and was complete by 9500cal yr BP. Deglaciation of the west and east sides of the Antarctic Peninsula ice sheet occurred at different times and rates, but was largely complete by the Early Holocene. At that time ice shelves were less extensive on the west side of the Antarctic Peninsula than they are today. The message from the past is that individual glacier drainage basins in Antarctica respond in different and distinctive ways to global climate change, depending on the link between regional topography and climate setting.

Journal Article↗
PubMed1999

Measurements of Past Ice Sheet Elevations in Interior West Antarctica.

A lateral moraine band on Mount Waesche, a volcanic nunatak in Marie Byrd Land, provides estimates of past ice sheet surface elevations in West Antarctica. Helium-3 and chlorine-36 surface exposure ages indicate that the proximal part of the moraine, up to 45 meters above the present ice surface, was deposited about 10,000 years ago, substantially later than the maximum ice extent in the Ross Embayment. The upper distal part of the moraine may record multiple earlier ice sheet high stands. A nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at Mount Waesche relative to the maximum ice extent in the Ross Sea. The glacial geologic evidence, coupled with the ice sheet model, indicates that the contribution of the Ross Sea sector of the West Antarctic Ice Sheet to Holocene sea level rise was only about 3 meters. These results eliminate West Antarctic ice as the principle source of the large meltwater pulse during the early Holocene.

Journal Article↗
PubMed2003

Rapid loss of bone mineral density of the femoral neck after cessation of ice hockey training: a 6-year longitudinal study in males.

UNLABELLED: The aim of this study was to evaluate the effect of training and reduced training on BMD in young ice hockey players during 6 years of follow-up. We found BMD gains in the femoral neck in the ice hockey group compared with controls. However, these gains were lost with reduced activity after cessation of career. INTRODUCTION: It has been suggested that increasing bone mass by intense physical activity during childhood and adolescence may decrease the risk of osteoporosis later in life. MATERIALS AND METHODS: In this longitudinal study, 43 ice hockey players (16.7 +/- 0.6 years) and 25 control subjects (16.8 +/- 0.3 years) were studied at baseline and after a mean period of 30 and 70 months. The groups did not differ in weight or height. Bone mineral density (BMD; g/cm2) was measured for total body, femoral neck, and spine using DXA. Volumetric BMD (vBMD; mg/cm3) of the femoral neck was estimated. RESULTS: The ice hockey players were found to have gained significantly more femoral neck BMD than controls (0.07 versus 0.03 g/cm2, p = 0.04) and to have gained femoral neck vBMD, whereas the controls did not (16 versus 0 mg/cm3, p = 0.049) between baseline and the first follow-up. At the first follow-up, the ice hockey players were found to have significantly higher BMD at the femoral neck and total body versus controls (p < 0.05). Between the first and second follow-ups, 21 ice hockey players stopped their active sports career. During this time period, these subjects lost significantly more femoral neck BMD (0.10 versus 0.02 g/cm2, p < 0.001) and femoral neck vBMD (38 versus 4 mg/cm3, p < 0.001) compared with the 22 ice hockey players who continued training. The former ice hockey players also lost significantly more neck vBMD (38 versus 14 mg/cm3, p = 0.009) compared with the controls during the same period. At the second follow-up, only the 22 ice hockey players who had continued their training were found to have significantly higher BMD at the femoral neck (p = 0.01), total body (p = 0.04), and spine (p = 0.02) compared with the controls. The former athletes were found to have intermediate BMD at all sites. CONCLUSION: In summary, we have demonstrated fast BMD loss at the femoral neck after decreased physical activity in young men. We conclude that ice hockey training during childhood and adolescence may not prevent the development of osteoporosis of the femoral neck later in life if the activity is not maintained.2003;18:1964-1969

Adolescent↗
PubMed1997

IL-1 beta convertase (ICE) does not play a requisite role in apoptosis induced in T lymphoblasts by Fas-dependent or Fas-independent CTL effector mechanisms.

Both IL-1beta convertase (ICE) and other members of the ICE-like family of proteases have been reported to play a role in Fas-mediated apoptosis. Con A-stimulated T lymphoblasts generated from splenocytes isolated from ICE-deficient H-2b mice were found to be more susceptible than wild-type lymphoblasts to DNA fragmentation induced by H-2b-specific CTL derived from normal or Fas ligand-deficient gld/gld mice. Trinitrophenyl (TNP)-modified, H-2b target cell-specific CTL were generated from perforin-deficient mice and were found to induce DNA fragmentation only in target cells expressing functional Fas receptors. Similar rates of DNA fragmentation were induced in TNP-modified ICE -/- and ICE +/+ T lymphoblast targets by perforin -/- TNP-modified, H-2b target cell-specific CTL. In addition, anti-Fas Abs induced apoptosis in thymocytes, Con A-stimulated spleen T cells, LPS-stimulated spleen B cells, and thymocytes from ICE -/- mice. However, DNA fragmentation induced by either allospecific FasL-defective CTL, or by perforin-deficient, TNP-modified, H-2b target cell-specific CTL was prevented in ICE -/- target cells loaded by electroporation with Ac-DEVD-CHO, an inhibitor of CPP32 and related ICE family proteases. These findings indicate that ICE does not play a requisite role in Fas-dependent or Fas-independent mechanisms of apoptosis induced in peripheral T lymphoblasts by CTL. However, both major pathways of CTL-induced apoptosis appear to be dependent on the enzymatic activity of other ICE family proteases.

Animals↗
PubMed1989

Seasonal variation in freeze tolerance and ice content of the tree frog Hyla versicolor.

Freeze tolerance and ice content of Hyla versicolor showed pronounced variation between summer (June) and winter (December). Summer frogs survived freezing at -3 degrees C for up to 9 hr and ice accumulation up to 50% of their total body water. A time course of ice formation indicated that an equilibrium level was reached in approximately 15 hr. Thus, the lethal ice content was less than the equilibrium ice content for these conditions (63.1%). A second group was induced to enter an overwintering condition by holding them through the summer and then subjecting them to a progressive reduction in temperature and photoperiod for 2 months. These frogs survived freezing for 48 hr at -3 degrees C. Their equilibrium ice content at this temperature was significantly lower (52.5%) than comparably treated summer animals. In the winter acclimatized group, frozen frogs had substantially higher blood glucose levels than unfrozen frogs (22.7 mumol/ml vs. 1.33 mumol/ml), but glycerol levels were not elevated after freezing. Freezing frogs conditioned for overwintering at -7 degrees C resulted in a higher equilibrium ice content (62.6%), but none survived. It is evident that in preparation for overwintering, frogs reduce the amount of ice formed at a given subzero temperature, but there is little indication of a substantial change in the total amount of ice tolerated.

Animals↗
PubMed2005

A study on the primary and secondary nucleation of ice by power ultrasound.

Several different investigations have been carried out to study the primary and secondary nucleation of ice by sonocrystallisation. Firstly, the primary nucleation of discrete ice crystals in a supercooled sucrose solution has been observed. For increasing concentrations of sucrose solutions from 0 to 45 wt%, the nucleation temperature consistently occurs at a higher nucleation temperature in the presence of ultrasound. The nucleation temperature also increases as the power output and duty cycle of a commercial ultrasonic horn are increased. Snap shot images of the bubble clouds obtained from the ultrasonic horn also show that the number of bubbles appears to increase as the ultrasonic output is increased. This suggests that the nucleation of ice is related to the power output and number of cavitation bubbles. The effect of a single bubble on the sonocrystallisation of ice is discussed. High-speed movies (1120 fps) have shown that the crystallisation appears to occur in the immediate vicinity of the single bubble. In most cases, many crystals are observed and it is not known whether a single ice crystal is being fragmented by the bubble or whether many crystals are being initiated. The bubble appears to undergo a dancing regime, frequently splitting and rejoining and also emitting some small microbubbles. A study on the secondary nucleation of ice in sucrose solutions has been carried out using a unique ultrasonic cold stage device. Images taken using a microscope system show that the pre-existing ice dendrite crystals can be broken up into smaller fragments by an ultrasonic field. Cavitation bubbles appear to be important during the fragmentation process, possibly melting any ice crystals in their path. Flow patterns around cavitation bubbles have also been observed, and these may be responsible for the fragmentation of ice crystals.

Crystallization↗
PubMed2003

Computational study on the function of water within a beta-helix antifreeze protein dimer and in the process of ice-protein binding.

Antifreeze proteins (AFPs) help many organisms protect themselves from freezing in subzero temperatures. The most active AFPs found to date are those from insects, which possess exceptionally regular beta-helical structures. On the ice-binding surface of these proteins, regularly arrayed water molecules are observed within the repeating Thr-Xxx-Thr motif, but the exact role of these water molecules remains unknown. In this work, we have employed a number of computational methods to examine the role of these water molecules in an AFP from Tenebrio molitor (TmAFP). Our investigation involved a combination of molecular and quantum mechanical approaches. Properties such as stability, interaction energy, orbital overlap, and conformational analysis of various systems, including TmAFP-water, TmAFP-water-ice, and TmAFP-ice, were systematically evaluated and compared. The regularly arrayed water molecules were found to remain associated with TmAFP before ice binding, demonstrating that they are an intrinsic part of the protein. These water molecules may assist TmAFP in the process of ice recognition and binding. However, after facilitating the initial stages of ice recognition and binding, these water molecules are excluded in the final formation of the AFP-ice complex. The departure of these water molecules enables a better two-dimensional match between TmAFP and ice. These results agree with experimental observations showing that although these water molecules are aligned with the ice-binding hydroxyl groups of Thr residues in one dimension, they are in fact positioned slightly off in the second dimension, making a good two-dimensional match impossible.

Animals↗
PubMed1999

An ice test for the diagnosis of myasthenia gravis.

OBJECTIVE: To determine whether ice application to a ptotic eyelid can differentiate myasthenic from nonmyasthenic ptosis. DESIGN: Prospective, multicenter, nonrandomized, comparative trial. PARTICIPANTS: Twenty patients with myasthenia gravis (MG) and ptosis were evaluated in the neuro-ophthalmology service. CONTROL SUBJECTS: Twenty patients with nonmyasthenic ptosis evaluated in the same locale. METHODS: Palpebral fissures were measured before and immediately after a 2-minute application of ice to the ptotic eyelid. MAIN OUTCOME MEASURES: The difference in palpebral fissures in millimeters before and after ice application. Two or more millimeters of improvement after ice application was considered a positive ice test result. RESULTS: A positive ice test result was noted in 16 of the 20 (80%) patients with MG and in none of the 20 patients without MG (P < 0.001). Of the 4 patients with MG and complete ptosis, 3 had a negative ice test result. CONCLUSIONS: The ice test is a simple, short, specific, and relatively sensitive test for the diagnosis of myasthenic ptosis. The sensitivity of the ice test in patients with complete ptosis decreases considerably.

Adult↗
PubMed1997

Microbiological quality of ice in hospital and community.

A survey was undertaken in response to a report of a clinical infection which had been related to an ice-making machine on a hospital ward. A detailed study of the ice microflora of 27 ice-making machines was performed. In a subsequent survey, ice samples (N = 194) from establishments such as bars and hotels were examined for bacterial indicators of hygiene. Samples from hospital ice-making machines yielded low numbers of a wide range of potentially opportunistic micro-organisms, many of environmental rather than clinical origin. For ice sampled in the community, the total aerobic plate count (TAPC) at 37 degrees C for 95% of the samples was < 500 cfu/mL, and at 22 degrees C 75% had < 500 cfu/mL. Examination for coliforms showed that 69% of samples contained no coliforms, but 20% contained > 100 coliforms/100 mL. Escherichia coli was detected in three samples but in very low numbers. This report investigates the relevance of ice machines to the control of hospital infection, the hygiene of ice in the community, discusses the microbiological quality of ice and proposes possible guidelines.

Bacterial Infections↗
PubMed1996

Refined solution structure of type III antifreeze protein: hydrophobic groups may be involved in the energetics of the protein-ice interaction.

BACKGROUND: Antifreeze proteins are found in certain fish inhabiting polar sea water. These proteins depress the freezing points of blood and body fluids below that of the surrounding sea water by binding to and inhibiting the growth of seed ice crystals. The proteins are believed to bind irreversibly to growing ice crystals in such a way as to change the curvature of the ice-water interface, leading to freezing point depression, but the mechanism of high-affinity ice binding is not yet fully understood. RESULTS: The solution structure of the type III antifreeze protein was determined by multidimensional NMR spectroscopy. Twenty-two structures converged and display a root mean square difference from the mean of 0.26 A for backbone atoms and 0.62 A for all non-hydrogen atoms. The protein exhibits a compact fold with a relatively large hydrophobic core, several short and irregular beta sheets and one helical turn. The ice-binding site, which encompasses parts of the C-terminal sheet and a loop, is planar and relatively nonpolar. The site is further characterized by the low solvent accessibilities and the specific spatial arrangement of the polar side-chain atoms of the putative ice-binding residues Gln9, Asn14, Thr15, Thr18 and Gln44. CONCLUSIONS: In agreement with the adsorption-inhibition mechanism of action, interatomic distances between active polar protein residues match the spacing of water molecules in the prism planes (¿10&1macr;0¿) of the hexagonal ice crystal. The particular side-chain conformations, however, limit the number and strength of possible proten-ice hydrogen bonds. This suggests that other entropic and enthalpic contributions, such as those arising from hydrophobic groups, could play a role in the high-affinity protein-ice adsorption.

Animals↗
PubMed2002

Contribution of hydrophobic residues to ice binding by fish type III antifreeze protein.

Type III antifreeze protein (AFP) is a 7-kDa globular protein with a flat ice-binding face centered on Ala 16. Neighboring hydrophilic residues Gln 9, Asn 14, Thr 15, Thr 18 and Gln 44 have been implicated by site-directed mutagenesis in binding to ice. These residues have the potential to form hydrogen bonds with ice, but the tight packing of side chains on the ice-binding face limits the number and strength of possible hydrogen bond interactions. Recent work with alpha-helical AFPs has emphasized the hydrophobicity of their ice-binding sites and suggests that hydrophobic interactions are important for antifreeze activity. To investigate the contribution of hydrophobic interactions between type III AFP and ice, Leu, Ile and Val residues on the rim of the ice-binding face were changed to alanine. Mutant AFPs with single alanine substitutions, L19A, V20A, and V41A, showed a 20% loss in activity. Doubly substituted mutants, L19A/V41A and L10A/I13A, had less than 50% of the activity of the wild type. Thus, side chain substitutions that leave a cavity or undercut the contact surface are almost as deleterious to antifreeze activity as those that lengthen the side chain. These mutations emphasize the importance of maintaining a specific surface contour on the ice-binding face for docking to ice.

Amino Acid Sequence↗
PubMed1988

Phenomena at the advancing ice-liquid interface: solutes, particles and biological cells.

Ice formation in aqueous solutions and suspensions involves a number of significant changes and processes in the residual liquid. The resulting effects were described concerning the redistribution of dissolved salts, the behaviour of gaseous solutes and bubble formation, the rejection and entrapment of second-phase particles. This set of conditions is also experienced by biological cells subjected to freezing. The influences of ice formation in that respect and their relevance for cryopreservation were considered as well. A model of transient heat conduction and solute diffusion with a planar ice front, propagating through a system of finite length was found to be in good agreement with measured salt concentration profiles. The spacing of the subsequently developing columnar solidification pattern was of the same order of magnitude as the pertubation wavelengths predicted from the stability criterion. Non-planar solidification of binary salt solutions was described by a pure heat transfer model under the assumption of local thermodynamic equilibrium. The rejection of gaseous solutes and the resulting gas concentration profile ahead of a planar ice front has been estimated by means of a test bubble method, yielding a distribution coefficient of 0.05 for oxygen. The nucleation of gas bubbles has been observed to occur at slightly less than 20-fold supersaturation. The subsequent radial growth of the bubbles obeys a square-root time dependence as expected from a diffusion controlled model until the still expanding bubbles become engulfed by the advancing ice-liquid interface. The maximum bubble radii decrease for increasing ice front velocities. The transition between repulsion and entrapment of spherical latex particles by an advancing planar ice-front has been characterized by a critical value of the velocity of the solidification interface. The critical velocity is inversely proportional to the particle radius as suggested by models assuming an undisturbed ice front. The increase of the critical velocity for increasing thermal gradients shows good agreement with a theoretically predicted square-root type of dependence. Critical velocities have also been measured for yeast and red blood cells. The effect of freezing on biological cells has been analyzed for human lymphocytes and erythrocytes. The reduction of cell volume observed during non-planar freezing agrees reasonably well with shrinkage curves calculated from a water transport model. The probability of intracellular ice formation has been characterized by threshold cooling rates above which the amount of water remaining within the cell is sufficient for crystallization.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Physiological Phenomena↗
PubMed2003

Reversible binding of the HPLC6 isoform of type I antifreeze proteins to ice surfaces and the antifreeze mechanism studied by multiple quantum filtering-spin exchange NMR experiment.

Antifreeze proteins (AFPs) protect organisms from freezing damage by inhibiting the growth of seed-ice crystals. It has long been hypothesized that irreversible binding of AFPs to ice surfaces is responsible for inhibiting the growth of seed-ice crystals as such a mechanism supports the popularly accepted Kelvin effect for the explanation of local freezing-point depression. However, whether the binding is reversible or irreversible is still under debate due to the lack of direct experimental evidence. Here, we report the first direct experimental result, by using the newly developed multiple quantum (MQ) filtering-spin exchange NMR experiment, that shows that the binding of HPLC6 peptides to ice surfaces is reversible. It was found that the reversible process can be explained by the model of monolayer adsorption. These results suggest that the Kelvin effect is not suitable for explaining the antifreeze mechanism, and direct interactions between the peptides and the ice-surface binding sites are the driving forces for the binding of AFPs to ice surfaces. We propose that there exists a concentration gradient of AFP from an ice-binding surface to the solution due to the affinity of ice surfaces to AFPs. This concentration gradient creates a dense layer of AFP in contact with the ice-binding surface, which depresses the local freezing point because of the colligative property, but not the Kelvin effect.

Antifreeze Proteins, Type I↗
PubMed2004

Ultrastructure in frozen/etched saline solutions: on the internal cleansing of ice.

Seawater, with its 3.5% salt content, freezes into hexagonal ice (Ih) that encloses concentrated brine within its matrix. When unsubmerged sea ice reaches a certain height and temperature, the brine drains downward through narrow channels. This mechanism was now modeled by frozen 2-3.5% saline as investigated by cryo-etch high-resolution secondary electron microscopy. Thus, saline was either plunge-frozen in liquid ethane at -183 degrees C or else high-pressure frozen to -105 degrees C in 5-6 ms. Ice from a freshly exposed surface was then subjected to a high-vacuum sublimation ("etching"), a procedure that removes pure bulk ice in preference to ice from frozen hydrated salt. After chromium-coating the etched surface with a 2-nm film, the sample was examined by cryo-HRSEM. Granular icy "fences" were seen surrounding empty areas where amorphous ice had originally resided. Since the fences, about 1-2 mum high, survived the etching, it is likely that they consist of frozen brine. The presence of such fences suggests that, during freezing, saline can purge itself of salt with remarkable speed (5-6 ms). Alternatively, channels (perhaps routed around submicroscopic crystallites of cubic ice (Ic) embedded in the amorphous ice at -105 degrees C) can guide the migration of salt to the periphery of ice patches. Macromolecules fail to form fences because they diffuse too slowly or because they are too large to pass through the channels.

Freeze Etching↗
PubMedDate not supplied

Health effects resulting from nitrogen dioxide exposure in an indoor ice arena.

We investigated an outbreak of acute respiratory illness among adolescent ice-hockey players in an indoor ice arena in Stockholm that had a propane-powered ice-resurfacing machine. We administered questionnaires to all players, as well as to a reference group that had played ice hockey in indoor arenas with electric ice-resurfacing machines. In the exposed group, 55 subjects (55.6%) experienced acute respiratory symptoms, compared with 4 (7.1%) in the reference group (relative risk = 7.8; 95% confidence interval = 3.0, 20.3). The risk for pulmonary symptoms increased as time spent on the ice increased. Levels of nitrogen dioxide up to 2358 microg/m3 (1250 ppb) were detected during simulated conditions of the incident. The most likely cause of the outbreak was the high level of nitrogen dioxide that resulted from poor ventilation and a malfunctioning ice-resurfacing machine. Propane-fueled ice-resurfacing machines should not be used in indoor ice arenas.

Adolescent↗
PubMed1968

Ultraviolet bactericidal irradiation of ice.

We investigated the germicidal activity of 2,537 A ultraviolet (UV) radiation on bacteria in ice cubes of varying thickness and in aqueous suspensions beneath an ice layer. The test bacteria used were Escherichia coli, Serratia marcescens, Bacillus subtilis, and Sarcina lutea; aqueous suspensions of the selected organisms were frozen into ice cubes, 2 mm to 30 mm thick, at -20 C. The cubes were irradiated for 1 min, whereas the suspensions of bacteria were placed beneath an ice block (19 cm thick) and were irradiated for 0.5 to 15 min. In both groups of experiments, the standard plate count method was used to compare the number of bacteria surviving the UV treatment with the number of bacteria in the untreated controls. The results showed that 1 min of UV treatment killed as many as 97% of the gram-negative and at least 60% of the gram-positive test bacteria (freezing survivors) frozen in ice cubes 30-mm thick. Within 15 min, UV light transmitted through a 19-cm thick ice block inactivated 98% of the bacteria suspended in the buffer solution. We concluded that the UV rays were able to penetrate at least 19 cm of ice and still retain enough energy to kill bacteria. However, the UV penetration depended greatly on the optical quality of the ice. Although it was not the purpose of these experiments to find a practical method for sanitizing ice, the results of this study and of our other unpublished experiments indicate that UV light has adequate penetrating power to be considered practical in certain selected applications.

Bacillus subtilis↗
PubMed2004

Comparison of carbon monoxide levels during heating of ice and water to boiling point with a camping stove.

OBJECTIVES: To determine whether using a camping stove to bring a pan of ice to boiling point produces higher carbon monoxide (CO) concentration than would bringing a pan of water to boiling point. The hypothesis was that ice would cause greater CO concentration because of its greater flame-cooling effect and, consequently, more incomplete combustion. METHOD: This was a randomized, prospective observational study. After an initial pilot study, CO concentration was monitored during 10 trials for each of ice and water. A partially ventilated 200-L cardboard box model was developed and then used inside a chamber at -6 degrees C. Ice temperature and volume, water temperature and volume, pan size, and flame characteristics were all standardized. Temperature of the heated medium was monitored to determine time to boiling point. Carbon monoxide concentration was monitored every 30 seconds for the first 3 minutes, then every minute until the end of each 10-minute trial. RESULTS: There was no significant difference (P > .05) in CO production levels between ice and water. Each achieved a similar mean plateau level of approximately 400 ppm CO concentration with a similar rate of rise. However, significantly higher (P = .014) CO concentration occurred at 4 and 5 minutes when the flame underwent a yellow flare; this occurred only on 3 occasions when ice was the medium. CONCLUSION: There were no significant differences for CO production between bringing a pan of ice or water to boiling point. In a small number of ice trials, the presence of a yellow flame resulted in high CO concentration. Yellow flares might occur more often with ice or snow melting, but this has not been proven.

Air Pollutants↗
PubMed1985

Relationships between ice crystal size, water content and proton NMR relaxation times in cells.

Biological specimens were frozen under controlled conditions. We questioned how the size of ice crystals, as measured in cryosectioned and cryoadsorbed sections of these biological specimens, relates to the water content and to the proton NMR relaxation times (T1 and T2) of the unfrozen specimens. The results permit the following conclusions: After rapid freezing in liquid propane cooled in a liquid nitrogen bath, the average size of ice crystals at distances of 150 microns or more from the surface of a particular tissue was always the same. Thus, the average size of the ice crystals was found to be characteristic of the type of biological tissue studied. Linear regression analysis showed average ice crystal size to have a significant correlation coefficient to T1 relaxation time and to water content. Specifically ice crystal size increased with T1 relaxation time and with water content. Multiple regression and path analysis demonstrated a positive correlation between the T1 relaxation time and the ice crystal size variation. Path analysis showed that both water content and T2 relaxation time were less directly correlated with ice crystal size. The findings from the path analysis and other observations show that the average size of ice crystals in subcellular compartments is best predicted by the proton T1 relaxation time. A working model is put forth to explain differences in ice crystal size observed between specimens enriched in globular or in parallel filamentous proteins.

Animals↗