The Putative Roles of Adenosine in Insulin- and Exercise-Mediated Regulation of Glucose Transport and Glycogen Metabolism in Skeletal Muscle

Skeletal muscle is the primary site of whole-body glucose disposal and is vital in determining the overall insulin sensitivity and carbohydrate management. Insulin and physical exercise are important stimuli for muscle glucose transport and glycogen metabolism. While it is known that both insulin and contraction stimulate muscle glucose uptake and glycogen metabolism, the post-receptor mechanisms are not completely understood. Local metabolic factors, such as adenosine, have been suggested to play a role in insulin and contraction regulation of carbohydrate metabolism in skeletal muscle. While adenosine has clearly been shown to potentiate insulin-stimulated glucose transport in adipocytes and heart muscle, its role in carbohydrate metabolism in skeletal muscle is less clear, with numerous diverging findings published to date. This review article summarizes findings on the putative roles of adenosine in insulin and exercise-mediated regulation of carbohydrate metabolism and the signalling pathways proposed to be central to these metabolic stimuli in skeletal muscle. Key words: carbohydrate metabolism, adenosine receptor, signal transduction, insulin resistance, diabetes mellitus, obesity

Selected physiological responses of kudzu to different chromium concentrations

This study was designed to evaluate the potential use of kudzu (Pueraria montana var. lobata) as a phytoremediator to reduce Cr (VI) contamination. In addition, the effect of Cr concentrations of 4, 8, and 12 mg L–1 on kudzu growth, gas exchange, pigment concentration, and carbohydrate accumulation were evaluated. In general, Cr uptake by kudzu was increased as Cr concentration increased in the growing media. Most of the Cr taken up by kudzu was accumulated in the root as indicated by the significantly higher ratio of root/shoot Cr concentrations at increasing Cr levels in the root environment. Kudzu growth, photosynthetic rate, and chlorophyll a and b concentrations declined as the Cr concentration increased. The decrease in photosynthesis was independent of the internal carbon dioxide. Anthocyanin was found to increase as Cr concentration gradually increased from 4 to 12 mg L–1. Kudzu clearly demonstrated its ability to survive at Cr concentrations up to 8 mg L–1 in the root environment. Kudzu, therefore, can be considered as a replacement crop in areas of Cr contamination falling within the concentration range of this study. Key words: Carbohydrate, chromium uptake, photosynthesis, phytoremediation

Effects of reproduction and artificial herbivory on vegetative growth and resource levels in deciduous and evergreen dwarf shrubs

Effects of reproduction (production of flowers and berries) and artificial herbivory of different phenological stages on deciduous bilberry (Vaccinium myrtillus L.) and evergreen lingonberry (Vaccinium vitis-idaea L.) were investigated to determine differences in allocation patterns and recovery ability between these species. Vegetative growth and concentration of sugars, starch, and nitrogen were measured in ramets at the end of the growing season. Statistical comparisons were made between the treatments and damage times, but not between the species, as these were manipulated at different sites within the same forest. Reproduction reduced the vegetative growth significantly in lingonberry, whereas the fertile bilberry ramets grew even more than the sterile ones. The bilberry produced new shoots as a response to simulated herbivory, which significantly decreased carbohydrate levels in tissues. The evergreen lingonberry produced less shoots, and carbohydrate levels increased significantly. Nitrogen concentration either remained unchanged or increased in both species. For both species, time of damage affected the carbon and nitrogen levels as well as the ability to regrow. The species have developed different strategies to overcome the costs of sexual reproduction and herbivory damage, apparently as a result of the different resource allocation patterns and different architectural constraints for shoot development. The evergreen lingonberry grows slowly and conserves resources, whereas the deciduous bilberry allocates resources to increase the photosynthesizing biomass, which increases the potential of future survival, growth, and reproduction. Key words: carbohydrate, clipping, deblossoming, defoliation, nitrogen, Vaccinium.

Evidence for proliferation of Enterobacter cloacae on carbohydrates in cucumber and pea spermosphere

Enterobacter cloacae EcCT501 grew on a variety of mono- and oligo-saccharides in vitro but did not grow on any of the polysaccharides tested. Carbohydrates found in seed exudates supported growth as did major monosaccharide constituents of seed storage carbohydrates and various seed-associated oligosaccharides. In addition, a rifampicin-resistant mutant of E. cloacae EcCT501, strain 501R3, grew on several of these mono- and oligo-saccharides in a natural gravely loamy sand soil. Glycosidase activities were detected in E. cloacae EcCT501 cultures that have the potential to degrade carbohydrate seed exudates and the oligosaccharide components of seed storage carbohydrates. Aqueous extracts from corn and pea seed induced activities of α-galactosidase 15- and 18-fold, respectively. Activities of α-glucosidase, β-glucosidase, and β-xylosidase were slightly induced by corn and pea seed extracts. Induction of these glycosidase activities by these extracts is consistent with their involvement in spermosphere proliferation. No carbohydrate depolymerase activities were detected. Strain A-11, which was isolated after mutation of strain 501R3 with transposon mini-Tn5 Km, lost the ability to grow on or had a reduced growth rate on several carbohydrates. Strain A-11 was similar to strain 501R3 in other nutritional tests. In cucumber spermosphere proliferation assays populations of strains 501R3 and A-11 were significantly different (P = 0.001) at 20 and 45 h. Strain A-11 did not proliferate in cucumber spermosphere, while strain 501R3 increased in number 21-fold after 45 h. In pea spermosphere, populations of strains A-11 and 501R3 increased 345- and 690-fold, respectively, after 45 h (significantly different at P = 0.1). These data are consistent with the hypothesis that spermosphere mono- and oligo-saccharides have roles as nutrients during spermosphere proliferation by E. cloacae. Key words: carbohydrate nutrition, spermosphere proliferation, glycosidase.

INFLUENCE OF READILY-AVAILABLE CARBOHYDRATES ON MAGNESIUM ABSORPTION IN RUMINANTS

Supplementing orchardgrass (Dactylus glomerata L.) hay with glucose, sucrose, lactose or starch increased apparent magnesium absorption in sheep. In subsequent experiments ruminai infusion of a glucose solution increased apparent magnesium absorption, but infusing hydrochloric acid (HCl) or a mixture of buffered or unbuffered propionate and butyrate in solution did not affect absorption. Key words: Carbohydrate, hypomagnesemic tetany, magnesium absorption, sheep.