Absence of heterothermy in the European red squirrel (Sciurus vulgaris)

The European red squirrel Sciurus vulgaris inhabits areas which undergo profound seasonal declines in food availability and ambient temperature. We measured the body temperature (T_b) of free-ranging S. vulgaris over the course of one year to examine its thermoregulatory strategies and found no evidence of heterothermy, with T_b never dropping below 36.7 °C. A lower average T_b and a reduced active phase are likely to have resulted in some energetic savings, sufficient for survival during the particularly mild winter with unhindered access to food stores. We cannot exclude that a different T_b pattern may be seen in energetically more demanding years, but we can confirm that heterothermy is not an obligatory behaviour in this species to counter energetic bottlenecks. Either S. vulgaris is indeed a strict homeotherm, or the need for torpor is flexibly adjusted.     

Bacterial cell wall-degrading enzymes induce basidiomycete natural product biosynthesis

Natural products play a vital role for intermicrobial interactions. In the basidiomycete arena an important representative is variegatic acid, a lactone natural product pigment whose ecological relevance stems from both inhibiting bacterial swarming and from indirect participation in breakdown of organic matter by brown-rotting fungi. Previous work showed that the presence of bacteria stimulates variegatic acid production. However, the actual external molecular trigger that prompts its biosynthesis in the mushroom hyphae remained unknown. Here, we report on the identification of Bacillus subtilis subtilisin E (AprE) and chitosanase (Csn) as primary inducers of pulvinic acid pigment formation. Using the established co-culture system of B. subtilis and Serpula lacrymans, we used activity-guided FPLC-based fractionation of B. subtilis culture supernatants and subsequent peptide fingerprinting to identify candidates, and their role was corroborated by means of a pigment production assay using heterologously produced chitosanase and subtilisin. B. subtilis mutants defective in either the aprE or the csn gene still triggered pigmentation, yet to a lower degree, which points to a multicausal scenario and suggests the combined activity of these cell wall polymer-attacking enzymes as true stimulus.     

Asparaginase and glutaminase activities in culture media containing dialyzed fetal calf serum

Summary Degradation of asparagine in media containing dialyzed fetal calf serum has been shown to be the result of asparaginase, which is active even at 4°C. The asparaginase activity of undialyzed fetal calf serum is only one-tenth of that found in the dialyzed serum. Glutaminase activity was also demonstrated in the medium containing dialyzed fetal calf serum. Minor changes in some other amino acids were also observed. This work was supported in part by Grant CA02568, National Cancer Institute, National Institutes of Health.     

Comparative length-tension relationship of urinary bladder strips from hamsters, rats, guinea-pigs, rabbits and cats

1. Comparative passive tension-active tension curves were constructed for urinary bladder body strips from hamster, rat, guinea-pig, rabbit and cat. 2. Equally sized strips from rabbit and cat bladders had a significantly greater mass and cross-sectional area than strips from other species. 3. There was a greater change in cross-sectional area of strips from rabbit and cat bladders with increasing length than in strips from other species. 4. Cat bladder strips developed a significantly greater absolute active tension than did strips from all other species at passive tensions greater than 5 g. 5. The length-tension relationships of the urinary bladder differs from skeletal or vascular smooth muscle in that there is no significant decrease in active tension at strip lengths greater than L0. 6. The ability of the urinary bladder to generate active tension at tissue lengths considerably greater than L0 is a prime importance in the physiological role of the urinary bladder to accommodate and store urine.     

Creatine kinase activity in normal and hypertrophied rabbit urinary bladder tissue (following partial outlet obstruction)

The urinary bladder depends on intracellular ATP to support a number of essential intracellular processes including contraction. The concentration of ATP is maintained by mitochondrial oxidative phosphorylation, cytosolic glycolysis and the cytosolic activity of creatine kinase, the enzyme that catalysis the rapid transfer of a phosphate from creatine phosphate (CP) to ADP resulting in the formation of ATP.Prior studies in this lab and others have demonstrated that mitochondrial respiration is significantly lower in hypertrophied bladder tissue (induced by partial outlet obstruction of the white New Zealand Rabbit). In addition to decreased mitochondrial respiration, there are significant increases in glycolysis and lactic acid formation in the hypertrophied tissue.In view of the increased glycolysis and decreased mitochondrial function in the hypertrophied tissue, and the importance in creatine kinase in maintaining cytosolic levels of ATP, the current study was designed to determine if outlet obstruction induces any changes in the activity of creatine kinase.The following is a summary of the results: 1) The bladder mass increased from 2.2 ± 0.2 gm to 11.5 ±1.6 gm at 7 days following outlet obstruction. 2) The intracellular concentrations of both ATP and CP were significantly reduced in the bladder tissue following 7 days of obstruction. 3) The percent of protein (per tissue mass) was significantly lower in the obstructed bladders, although the percent of soluble protein was similar. 4) Creatine kinase activity of control bladders showed linear kinetics with a V_max = 1120 nmoles/mg protein/4 min and K_m = 147 µM CP. 2) The creatine kinase activity of obstructed bladders also displayed linear kinetics with a V_max = 1125 nmoles/mg protein/4 min tissue, and K_m = 276 µM CP.These studies demonstrate that whereas both control and obstructed bladders have virtually identical maximum creatine kinase activities, the K_m for the obstructed tissue is significantly higher than the K_m for the control tissue. This may indicate that under cellular conditions (at sub-maximum substrate concentrations), the creatine kinase activity of the obstructed bladders may be significantly lower than the activity of the control bladders. In addition, the reduced tissue concentrations of ATP and CP would certainly be consistent with the reduced functional response to bethanechol and field stimulation.