Structural changes in mammalian cells associated with cooling to-79 degree C

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.

Susceptibility of human foetal brain tissue to cool- and freeze-storage

Human second trimester foetal brain tissue was stored for a period of 1-6 weeks under various conditions in an attempt to evaluate factors influencing its susceptibility (cell loss) and survivability. Post-storage viability of mesencephalon, striatum, cerebellum and occipital cortex was assessed by a protocol combining vital staining with cell density counts so that tissue viability and cell loss could be evaluated simultaneously; tissue survivability was evaluated by cell culture. A significant amount of cell loss occurred after 24 h storage at room temperature, after one week at 4 degrees C and by two weeks at -20 degrees C in all structures; storage at -196 degrees C resulted in 17-21% cell loss at the end of a 6 week period. At -20 degrees C the cryoprotective effect of 20% FCS was equivalent to that of 15% FCS + 7% DMSO combined, suggesting potential use of serum in replacement of chemical additives. The procedure for removal of DMSO was critical to cell viability and survivability: single step dilution led to 27-39% greater cell loss than slow, multi-step dilutions. In comparison to fresh, non-stored tissue, immunocytochemical characterization of in vitro propagated stored tissue revealed no changes in the populations of major constituent cell types including neurones, dopaminergic neurones, glial and fibroblast cells. These results provide information on possible conditions under which transplant tissue can be satisfactorily stored depending on the prevailing requirements.

X-ray diffraction of myelin membrane. II. Determination of the phase angles of the frog sciatic nerve by heavy atom labeling and calculation of the electron density distribution of the membrane

The phase signs of the five main X-ray reflections from normal frog sciatic nerve have been determined as all positive using a technique of labeling with very small amounts of heavy metal. The changes in intensity of the individual reflections were studied as a function of uptake of metal label by the membrane. The possible localization of the metal label was decided from computer-analogue studies and from Patterson calculations. These phases are different from those determined by previous workers using techniques of trial of the best set of phases, or a step model, to give the best fit of the combined intensity data of normal and swollen myelin membranes. The electron density map has been calculated using eight reflections and their experimentally determined phases. The map shows an inner low electron density region which is different from that shown by earlier calculations. The center of the low electron density region shows a small region of increased electron density. However, without fixing absolute electron density levels in the map, it is not yet possible to allocate regions of low electron density to pure lipid or lipoprotein. The map shows the two sides of the membranes to be different in molecular structure without significant water spaces between the membranes.