Growth of an ice phase in frozen tissue studied by proton NMR-spectroscopy

Development of an ice phase in frozen tissue is a severe problem in cryo-ultramicrotomy. It is assumed that the growth-rate of such an ice phase is controlled by the mobility of the water molecules in the tissue. In order to verify this, wide-line nmr-spectroscopy has been performed on the protons of frozen whole blood, with and without protective agent, in the temperature range −100 °C- −40 °C. The molecular motion may be characterized by a correlation time, τ, which can be thought of as roughly the mean time between proton jumps. The value of τ can be approximately evaluated from the width of the proton resonance line. It is shown that τ varies rapidly with temperature, in a similar manner to maximum storage time for frozen blood in blood banks. Addition of glycerol increases τ at low temperature, which is consistent with its use as a protective agent in cryobiology. At high temperature, addition of glycerol reduces τ, which is in agreement with reported light-microscope observations on the growth-rate of an ice phase in the same temperature range, nmr-spectroscopy seems to be a useful tool in the further development of cryo-ultramicrotomy. However, to estimate the value in full, more data is required than is presented here.     

Characteristics of adenosine activity on adenine nucleotide metabolism of rat thymocytes

The effects of adenosine on adenine nucleotide metabolism in [14C]adenine-labeled rat thymocytes were studied. It was shown that adenosine increases the intracellular pool of adenine nucleotides, predominantly ATP, which is accompanied by marked acceleration of their catabolism and a release of labeled products (especially inosine, hypoxanthine and adenosine) from the thymocytes. The effect of adenosine depends on its concentration and manifests itself already at 10(-6) M. 2-Deoxycoformycin partly relieves the effect of adenosine on adenine nucleotide metabolism. Exogenous deoxyadenosine, inosine, hypoxanthine and adenine, unlike adenosine, do not significantly affect the adenine nucleotide catabolism and the label release from the cells. All the effectors under study strongly increase inosine transport from the thymocytes, and inhibit, with the exception of adenosine, the hypoxanthine release from the cells.