Muscle glycogen depletion during exercise at 9 degrees C and 21 degrees C

This study compared glycogen depletion in active skeletal muscle after light and moderate exercise in both cold and comfortable ambient conditions. Twelve male subjects (Ss) were divided into two groups equally matched for the submaximal exercise intensity corresponding to a blood lactate concentration of 4 mM (W4) during cycle exercise. On two separate days Ss rested for 30 min at ambient temperatures of either 9 degrees C or 21 degrees C, with the order of temperature exposure being counter-balanced among Ss. Following rest a tissue specimen was obtained from the m. vastus lateralis with the needle biopsy technique. Six Ss then exercised on a cycle ergometer for 30 min at 30% W4 (range = 50 - 65 W) while the remaining group exercised at 60% W4 (range = 85 - 120 W). Another biopsy was taken immediately after exercise and both samples were assayed for glycogen content. Identical procedures were repeated for the second environmental exposure. No significant glycogen depletion was observed in the Ss exercising at 30% W4 in 21 degrees C, but a 23% decrease (p = 0.04) was observed when the same exercise was performed at 9 degrees C. A 22% decrease (p = 0.002) in glycogen occurred in the 60% W4 group at 21 degrees C, which was not significantly different from that observed during the same exercise at 9 degrees C. The results suggest that muscle substrate utilization is increased during light exercise in a cold environment as compared to similar exercise at a comfortable temperature, probably due to shivering thermogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chloroethene biodegradation in sediments at 4 degrees C

Microbial reductive dechlorination of [1,2-14C]trichloroethene to [14C]cis-dichloroethene and [14C]vinyl chloride was observed at 4 degrees C in anoxic microcosms prepared with cold temperature-adapted aquifer and river sediments from Alaska. Microbial anaerobic oxidation of [1,2-14C]cis-dichloroethene and [1,2-14C]vinyl chloride to 14CO2 also was observed under these conditions.     

Freeze-fracturing in ultrahigh vacuum at -196 degrees C

Conventional freeze-etching is carried out in a vacuum of approximately 10(-6) torr and at a specimen temperature of -100 degrees C. The relatively poor topographic resolution of most freeze-etch replicas, and the lack of complementarity of morphological details in double replicas have been thought to be caused by structural distortions during fracturing, and radiation damage during replication. Both phenomena can be reduced by lowering the specimen temperature. To prevent condensation of residual gases (especially H2O) on the fracture faces at lower specimen temperature, an improved vacuum is required. Therefore, an ultrahigh vacuum freeze-fracture apparatus has been developed which allows fracturing and Pt/C-shadowing of specimens at -196 degrees C while maintaining a vacuum of 10(-9) torr. It consists of a modified Balzers BA 350 ultrahigh vacuum (UHV) unit, equipped with an airlock which enables the input of nonhoar-frosted specimens directly into the evacuated bell jar. A comparison of the paracrystalline plasmalemma structure in yeast cells portrayed by the conventional technique and by UHV-freeze-fracturing at -196 degrees C shows the improved topographic resolution which has been achieved with the new technique. The improvement is explained by less structural distortions during fracturing at lower temperatures. The particles of the paracrystalline regions on the P face are more regularly arranged and exhibit a craterlike substructure which corresponds with a ringlike depression in the E face. The optical diffraction patterns of these paracrystalline regions demonstrate the improvement of the structural record by showing well-defined third- and fourth-order spots.