Ventilatory responses to inspiratory threshold loading in humans

Normal alveolar ventilation tends to be maintained during external mechanical loading. The precise manner by which this occurs is unclear but may involve intrinsic mechanisms related to the muscular pump, neural influences, and chemoreceptor control. Recent observations suggest that submaximal threshold loads may result in hyperventilation. In this study we explicitly examined the respiratory effects of sustained threshold loading in normal subjects. We found that sustained threshold loading resulted in hyperventilation associated with high P100's (mouth pressure 100 ms after the start of an occluded breath) and increased tidal volumes but with little effect on duty cycle or respiratory rate. In addition, this increased respiratory motor output was sustained for 30-60 s after the load was removed. At very high threshold loads, hyperventilation failed to occur, despite increased P100's. We conclude that threshold loading results in increased respiratory motor output and hyperventilation, a response that is different from that observed with either resistive or elastic loads, and that the failure to hyperventilate at the higher loads may be the result of mechanical limitation.     

Regional localization of the human glutaminase (GLS) and interleukin-9 (IL9) genes by in situ hybridization.

Phosphate-activated glutaminase is found in mammalian small intestine, brain, and kidney, but not in liver. The enzyme initiates the catabolism of glutamine as the principal respiratory fuel in the small intestine, may synthesize the neurotransmitter glutamate in the brain, and functions in the kidney to help maintain systemic pH homeostasis. Interleukin-9 (IL9) is a relatively new cytokine that supports the growth of helper T-cell clones, mast cells, and megakaryoblastic leukemia cells. cDNA clones have recently been obtained for each of these genes. The human loci for phosphate-activated glutaminase (GLS) and IL9 have previously been mapped to chromosomes 2 and 5, respectively, by analysis of somatic cell hybrid DNAs. By using chromosomal in situ hybridization, we have regionally mapped GLS to 2q32----q34 and IL9 to 5q31----q35.     

Cytosolic thioredoxin reductase 1 is required for correct disulfide formation in the ER

Folding of proteins entering the secretory pathway in mammalian cells frequently requires the insertion of disulfide bonds. Disulfide insertion can result in covalent linkages found in the native structure as well as those that are not, so‐called non‐native disulfides. The pathways for disulfide formation are well characterized, but our understanding of how non‐native disulfides are reduced so that the correct or native disulfides can form is poor. Here, we use a novel assay to demonstrate that the reduction in non‐native disulfides requires NADPH as the ultimate electron donor, and a robust cytosolic thioredoxin system, driven by thioredoxin reductase 1 (TrxR1 or TXNRD1). Inhibition of this reductive pathway prevents the correct folding and secretion of proteins that are known to form non‐native disulfides during their folding. Hence, we have shown for the first time that mammalian cells have a pathway for transferring reducing equivalents from the cytosol to the ER, which is required to ensure correct disulfide formation in proteins entering the secretory pathway.     

Challenges and opportunities for comparative studies of survival rates: An example with male pinnipeds

Survival rates are a central component of life‐history strategies of large vertebrate species. However, comparative studies seldom investigate interspecific variation in survival rates with respect to other life‐history traits, especially for males. The lack of such studies could be due to the challenges associated with obtaining reliable datasets, incorporating information on the 0–1 probability scale, or dealing with several types of measurement error in life‐history traits, which can be a computationally intensive process that is often absent in comparative studies. We present a quantitative approach using a Bayesian phylogenetically controlled regression with the flexibility to incorporate uncertainty in estimated survival rates and quantitative life‐history traits while considering genetic similarity among species and uncertainty in relatedness. As with any comparative analysis, our approach makes several assumptions regarding the generalizability and comparability of empirical data from separate studies. Our model is versatile in that it can be applied to any species group of interest and include any life‐history traits as covariates. We used an unbiased simulation framework to provide “proof of concept” for our model and applied a slightly richer model to a real data example for pinnipeds. Pinnipeds are an excellent taxonomic group for comparative analysis, but survival rate data are scarce. Our work elucidates the challenges associated with addressing important questions related to broader ecological life‐history patterns and how survival–reproduction trade‐offs might shape evolutionary histories of extant taxa. Specifically, we underscore the importance of having high‐quality estimates of age‐specific survival rates and information on other life‐history traits that reasonably characterize a species for accurately comparing across species.     

The crystal structure of carnitine palmitoyltransferase 2 and implications for diabetes treatment

Carnitine palmitoyltransferases 1 and 2 (CPTs) facilitate the import of long-chain fatty acids into mitochondria. Modulation of the catalytic activity of the CPT system is currently under investigation for the development of novel drugs against diabetes mellitus. We report here the 1.6 A resolution structure of the full-length mitochondrial membrane protein CPT-2. The structure of CPT-2 in complex with the generic CPT inhibitor ST1326 ([R]-N-[tetradecylcarbamoyl]-aminocarnitine), a substrate analog mimicking palmitoylcarnitine and currently in clinical trials for diabetes mellitus treatment, was solved at 2.5 A resolution. These structures of CPT-2 provide insight into the function of residues involved in substrate binding and determination of substrate specificity, thereby facilitating the rational design of antidiabetic drugs. We identify a sequence insertion found in CPT-2 that mediates membrane localization. Mapping of mutations described for CPT-2 deficiency, a hereditary disorder of lipid metabolism, implies effects on substrate recognition and structural integrity of CPT-2.     

Patterns of extensive genetic differentiation and variation among European harbor seals (Phoca vitulina vitulina) revealed using microsatellite DNA polymorphisms

The harbor seal (Phoca vitulina) has the most extensive distribution of any phocid seal species. An analysis of population structure in this species across its European range was made using 7 phocid derived microsatellites in a sample of 1,029 individuals from 12 separate geographic areas. Despite the species potential for long-distance movement, significant genetic differentiation between areas was observed using an unbiased estimator of RST. Six distinct population units were identified: Ireland-Scotland, English east coast, Waddensea, western Scandinavia (Norway-Kattegat-Skagerrak-west Baltic), east Baltic, and Iceland. Little local substructuring is present along coastlines with a continuous distribution of breeding animals, but differentiation does increase with geographic distance. The degree of differentiation is greater over equivalent distances where the distribution is discontinuous, such as along coasts where breeding colonies are separated by large distances or by stretches of open sea. Patterns of population differentiation derived from microsatellites are very similar to those obtained from previous mitochondrial DNA analysis and suggest that philopatry in harbor seals operates over 300-500 km. In Europe, harbor seals have experienced a complex demographic history and patterns of population structure are likely to have been affected by natural environmental influences such as Pleistocene glaciations and epizootics. Comparison of Nm values from an unbiased estimator of RST, GST, and theta are consistent and, in some cases, may indicate populations where conditions deviate from the expectations of the RST model.      

Acute Sirolimus Overdose: A Multicenter Case Series

BackgroundThere are few data relating to sirolimus overdose in the medical literature. Our objectives were to describe all cases of overdose with sirolimus reported to Swiss, German and Austrian Poisons Centres between 2002-2013.MethodsAn observational case-series analysis was performed to determine circumstances, magnitude, management and outcome of sirolimus overdose.ResultsFive cases of acute sirolimus overdose were reported – three in young children and two in adults. Four were accidental and one was with suicidal intent. Two patients developed symptoms probably related to sirolimus overdose: mild elevation of alkaline phosphatase, fever and gastroenteritis in a 2.5-year-old male who ingested 3 mg, and mild changes in total cholesterol in an 18-year-old female after ingestion of 103 mg. None of these events were life-threatening. Serial blood concentration measurements were performed starting 24 h after ingestion of 103 mg in a single case, and these followed a similar pharmacokinetic time-course to measurements taken after dosing in the therapeutic range.ConclusionsAcute sirolimus overdose occurred accidentally in the majority of cases. Even large overdoses appeared to be well-tolerated, however children might be at greater risk of developing complications. Further study of sirolimus overdose is needed.