The temperature dependence of the deformation of bone

The deformation characteristics of compact bone have been measured as a function of temperature in the range from −58 to 90°C. At temperatures below 25°C elastic, anelastic and plastic contributions to the strain could be distinguished. The Young's modulus increased as the temperature was reduced, while the nonelastic component was approximately independent of temperature. An interpretation of these results is made in terms of an idealised hydroxyapatite-collagen composite. At temperatures higher than 50°C the deformation was compounded by non-equilibrium recovery and an irreversible change in the structure of bone.     

The phospholipid head-group orientation: effect on hydration and electrical conductivity.

The water adsorption isotherms have been obtained for egg phosphatidyl-ethanolamine when it is complexed to egg phosphatidylcholine and cholesterol, respectively. In the presence of phosphatidylcholine, the phosphatidylethanol amine water binding is changed to a strong binding as compared to when the phospholipid is in its uncomplexed form. Cholesterol increases the water adorbed by the phospholipid, however, it does not change the nature of the isotherm. Phosphatidylmonomethylethanolamine also exhibits a strong water binding. The electrical conductivity of these phospholipids has been measured concurrently with their hydration. Electrical activation energies have been obtained for the fully hydrated phospholipids and are a function of both the amount of water adsorbed and the orientation of the polar head-group. The results are discussed in terms of a model for water adsorption, previously put forth by the authors.     

The effect of temperature on membrane hydraulic conductivity

The objective of this study was to use the temperature dependence of water permeability to suggest the physical mechanisms of water transport across membranes of osmotically slowly responding cells and to demonstrate that insight into water transport mechanisms in these cells may be gained from easily performed experiments using an electronic particle counter. Osmotic responses of V-79W Chinese hamster fibroblast cells were measured in hypertonic solutions at various temperatures and the membrane hydraulic conductivity was determined. The results were fit with the general Arrhenius equation with two free parameters, and also fit with two specific membrane models each having only one free parameter. Data from the literature including that for human bone marrow stem cells, hamster pancreatic islets, and bovine articular cartilage chondrocytes were also examined. The results indicated that the membrane models could be used in conjunction with measured permeability data at different temperatures to investigate the method of water movement across various cell membranes. This approach for slower responding cells challenges the current concept that the presence of aqueous pores is always accompanied by an osmotic water permeability value, P(f)>0.01 cm/s. The possibility of water transport through aqueous pores in lower-permeability cells is proposed.     

The effect of the phase transition on the hydration and electrical conductivity of phospholipids.

Adsorption isotherms for various saturated phosphatidylcholines have been obtained. Lipids above and below their phase transition temperature differ only in the amount of water adsorbed and not in the nature of their adsorption isotherms. Cholesterol has an effect similar to that of increasing unsaturation in the hydrocarbon chains. Decreasing the length of the hydrocarbon chains for lipids below their phase transition temperature has no effect on the isotherms. If the chain length is short enough so that the lipids are above their transition temperature, however, a large increase in water adsorption occurs. All of the phospholipids exhibit a rapid increase of electrical conductivity for a few water molecules adsorbed per lipid molecule. All of the phospholipids show a saturation in conductivity at greater amounts of adsorbed water; the shape of the saturation region depends on whether the lipids are above or below their phase transition temperature. The activation energy for the electrical conductivity process depends on whether the hydrated lipids are in the "liquid-like" of the crystalline state, being lower for phospholipids in the liquid-like state. If the lipids are hydrated above their phase transition temperatures, their activation energies are lower than if they are hydrated below the transition temperature. Cholesterol lowers the activation energy. The phosphatidylcholines can be characterized by different activation energies, depending both upon their physical state and the presence of unsaturation in their hydrocarbon chains.     

The effect of gamma-irradiation on the viability of Cryptosporidium parvum

Cryptosporidium parvum is 1 of the major causative organisms in waterborne diarrheal illness. Not only does C. parvum spread ubiquitously in our environment, it is also highly resistant to harsh environmental conditions and disinfectants. Therefore, a control measure for this protozoon is urgently required. This study investigated the effect of gamma-irradiation, in the range of 1,000-50,000 Gy, on the viability of C. parvum oocysts. Oocyst viability was determined by a combined indirect immunofluorescence and nucleic acid staining and animal infectivity study. The proportion of viable oocysts estimated by nucleic acid staining ranged from 94.2 to 89.4% in the 0- to 10,000-Gy groups, whereas it was reduced significantly to 58.6 or 45.7% in the 25,000- or 50,000-Gy group, respectively, at 24 hr postirradiation. In an animal infectivity study, oocysts irradiated with less than 10,000 Gy induced infections in mice wherein there were low numbers of oocysts per gram of feces amounting to 8-10.8% of the values in control mice, whereas with 50,000 Gy-irradiated oocysts, no oocysts were produced in the mice. This study suggests that at least 50,000 Gy of gamma-irradiation is necessary for the complete elimination of oocyst infectivity in mice.     

Changes in thermal and electrical properties of bone as a result of 1 MGy-dose gamma-irradiation

Determination of temperature dependencies of electric conductivity and thermal properties by differential scanning calorimetry (DSC) allow to analyse the processes of charge and heat transport in the bone being a complex collagen-hydroxyapatite (HAP)-water system. Modification of the bone structure by high doses of gamma-radiation changes the electrical and thermal properties of the bone. Electrical conductivity (sigma) of the bone decreases with consecutive heating runs. The decrease in sigma observed for irradiated samples was explained by the scission of the main chain of collagen macromolecule. Irradiation decreased the hydration level in the bone, its denaturation temperature and increased both enthalpy and entropy of the denaturation process.     

Membrane potential of rat calvaria bone cells: dependence on temperature

The membrane potentials of bone cells derived from calvaria of new born rats was shown to be strongly dependent on temperature. When we lowered the temperature from 36 degrees C to 26 degrees C, cells with spontaneous resting membrane potentials (MP) of -80 to -50 mV depolarized (mean amplitude 8 mV; n = 33), and the membrane resistance increased by approximately 80% (n = 20). The temperature response depended on the actual MP, the reversal potential being in the range of -80 to -90 mV. With the application of ouabain (0.1-1 mmol/liter; n = 12), cells depolarized. Simultaneously, the reversal potential of the temperature response was shifted towards more positive values and approached the actual MP level of the cells. Consequently, the depolarization amplitudes induced by lowering temperature were reduced at spontaneous MP levels. The rise of the membrane resistance during cooling was unaffected. When the extracellular chloride concentration was reduced from 133 to 9 mmol/liter, temperature-dependent depolarizations persisted at spontaneous MP values (n = 5). The findings indicate that the marked effects of temperature changes on the MP of bone-derived cells are mainly determined by changes of the potassium conductance.