The effects of breathing different levels of O2 and CO2 on the diving responses of ducks (Anas platyrhynchos) and cormorants (Phalacrocorax auritus)

Summary The effects of breathing different levels of O₂ and CO₂ before forced dives were investigated in 5 dabbling ducks (White Pekin) and 5 deep divers (Double Crested Cormorants). Breathing and heart rates, blood gases, and blood pH, were monitored. After breathing air before diving, ducks exhibited a slow decrease in heart rate that reached a minimum of 20 beats·min⁻¹ after 50 s submergence. The development of bradycardia was retarded if the duck breathed a hyperoxic gas mixture before diving and was accelerated if the gas mixture was hypoxic and hypercapnic. The cormorants' diving heart rate decreased to a minimum of about 60 beats·min⁻¹ in less than 20 s and development of bradycardia was unaffected by different levels of O₂ and CO₂ breathed before diving. Consequently, bradycardia in forced dived cormorants was unrelated to changes in blood gases in the dives which suggests that intravascular chemoreceptors are unimportant in initiating diving bradycardia in cormorants.     

Concurrent measurement of (Na+,K+)-ATPase activity and lipid peroxides in rat brain following reversible global ischemia

Lipid peroxides, quantitated as lipid conjugated dienes, and (Na⁺,K⁺)-ATPase activity were assayed concurrently in brains of control rats and in three groups subjected to 30 min of reversible forebrain ischemia followed by 0, 1, and 4 hr of recirculation. Multiple small samples were taken from lateral, dorsolateral and medial cortex, hippocampus, thalamus and striatum following in situ freezing. (Na⁺,K⁺)-ATPase activity was elevated in hippocampus, dorsolateral and lateral cortex (P<0.10) and in thalamus (P<0.05) following 30 min ischemia. ATPase activity in medial cortex continued to increase during the first 1 hr of recirculation (P<0.10). Following 4 hr of recirculation, decreased enzyme activities were observed in all of these regions (lateral cortex and hippocampus,P<0.10). No changes in ATPase activity were observed in samples from striatum. Of the regional samples assayed for lipid peroxide content, the incidence of conjugated dienes as a function of recirculation time was 6% (0 hr), 23% (1 hr), and 17% (4 hr). For these samples, plots of normalized ATPase activity vs. tissue conjugated diene concentration revealed that normalized ATPase activity varied with recirculation time, but was independent of the magnitude of the lipid peroxidative process (expressed in terms of tissue conjugated diene concentration). These results suggest that disturbances in membrane structure and function presumed to arise from lipid peroxidation are not responsible for the behavior of the ATPase under the current in vivo conditions.     

Ipomoea aquatica as a vegetable crop in Hong Kong

The aquatic plant Ipomoea aquatica is grown in southeastern Asia as a summer leaf vegetable. It is particularly common in south China and Hong Kong, where it has a very ancient history. Two methods of cultivation are used in Hong Kong: the dry-land method utilizing raised beds and the wet-land method on flooded paddy-fields. During the summer months I. aquatica supplies up to 15% of local vegetable production.     

Vectorcardiographic Abnormalities Simulating Myocardial Infarction in the Normal Heart

During a study of the vectorcardiogram in the normal young heart, four individuals were found in whom the QRS loops, surprisingly, fulfilled the usual criteria for the diagnosis of myocardial infarction. These vectorcardiograms are described in detail. Two of the four electrocardiograms are within normal limits. These abnormal vectorcardiographic patterns are probably due to a congenital variant in left ventricular conduction. This rare condition is of clinical significance because it may result in diagnostic confusion in older patients.     

Mgat1-dependent N-glycans are essential for the normal development of both vertebrate and invertebrate metazoans

UDP-GlcNAc:α3-d-mannoside β1,2-N-acetylglucosaminyltransferase I (GnTI, encoded by Mgat1) first appeared in evolution at about the same time as metazoa suggesting that GnTI-dependent glycans are essential for the development of multicellular organisms. This review describes the effects of mutations in the Mgat1 gene on the development of Caenorhabditis elegans, Drosophila melanogaster and mice.     

Application of dynamic flux balance analysis to an industrial Escherichia coli fermentation

We have developed a reactor-scale model of Escherichia coli metabolism and growth in a 1000L process for the production of a recombinant therapeutic protein. The model consists of two distinct parts: (1) a dynamic, process specific portion that describes the time evolution of 37 process variables of relevance and (2) a flux balance based, 123-reaction metabolic model of E. coli metabolism. This model combines several previously reported modeling approaches including a growth rate-dependent biomass composition, maximum growth rate objective function, and dynamic flux balancing. In addition, we introduce concentration-dependent boundary conditions of transport fluxes, dynamic maintenance demands, and a state-dependent cellular objective. This formulation was able to describe specific runs with high-fidelity over process conditions including rich media, simultaneous acetate and glucose consumption, glucose minimal media, and phosphate depleted media. Furthermore, the model accurately describes the effect of process perturbations—such as glucose overbatching and insufficient aeration—on growth, metabolism, and titer.     

Neuromolecular computing: a new approach to human brain evolution

Evolutionary approaches in human cognitive neurobiology traditionally emphasize macroscopic structures. It may soon be possible to supplement these studies with models of human information-processing of the molecular level. Thin-film, simulation, fluorescence microscopy, and high-resolution X-ray crystallographic studies provide evidence for transiently organized neural membrane molecular systems with possible computational properties. This review article examines evidence for hydrophobic-mismatch molecular interactions within phospholipid microdomains of a neural membrane bilayer. It is proposed that these interactions are a massively parallel algorithm which can rapidly compute near-optimal solutions to complex cognitive and physiological problems. Coupling of microdomain activity to permenant ion movements at ligand-gated and voltage-gated channels permits the conversion of molecular computations into neuron frequency codes. Evidence for microdomain transport of proteins to specific locations within the bilayer suggests that neuromolecular computation may be under some genetic control and thus modifiable by natural selection. A possible experimental approach for examining evolutionary changes in neuromolecular computation is briefly discussed. Received: 2 October 1998 / Accepted in revised form: 19 March 1999     

The effect of tetrathiomolybdate on the metabolism of copper by hepatocytes and fibroblasts

Tetrathiomolybdate (TTM) has been examined for its effect on copper metabolism in mouse hepatocytes in primary culture and human fibroblasts. It decreased the amount of copper inside hepatocytes, decreased the rate of copper uptake by hepatocytes in a concentration dependent manner, and increased the copper efflux from the cells. TTM appeared to remove copper preferentially from the labile pool, but with a lower affinity than cage chelators. In fibroblasts, TTM only had a marginal effect on copper levels below a concentration of 100 microM and had no clear effect on the rate of copper uptake. TTM was not toxic to human fibroblasts, but in some preparations, a concentration of more than 50 microM was toxic to hepatocytes.