Comparative Biochemistry and Physiology Part A: Physiology最新文献

Studies of the hemoglobin system of fish of the suborder Notothenioidei have been extended to non-Antarctic species Pseudaphritis urvillii and Notothenia angustata. The two species belong to families that were the first to diverge within the suborder. The degree of amino acid sequence identity with Antarctic notothenioids and other non-Antarctic fish species is analyzed with respect to phyletic and ecological divergence.

Nitric oxide synthase-positive nerve cells have been found in most vertebrate classes and also some invertebrates, indicating an early evolutionary origin for the enzyme and its function as a neurotransmitter. The general distribution and inhibitory effect on motility of nitric oxide in the fish gut agrees well with studies from other vertebrates, but details may vary between species, suggesting variations in function. The coexistence with vasoactive intestinal polypeptide (VIP)/pituitary adenylate cyclase-activating polypeptide (PACAP) suggests a co-function in fish as in mammals, but this remains to be confirmed.

The hemolymph of aquatic invertebrates is the target of many environmental contaminants. Different events of the cellular immune response constitute potential models for the development of sensitive bioassays. Here, a new methodology is described to quantify in vitro spontaneous aggregation by Crassostrea gigas hemocytes. Preliminary assays indicated that the aggregation index was altered when the cells were incubated at low or high temperature. The chelator EDTA or the drug caffeine added to the medium were powerful inhibitors. The effects of xenobiotics actually found in polluted marine waters [tributyltin (TBT) and trace metals] were tested by exposure of either the cells or whole individuals and appeared as efficient potential inhibitors. A higher sensitivity to cadmium than to copper has been revealed. Exposure of individuals in the laboratory to pesticides or TBT at peak environmental concentrations resulted in moderate changes in hemocyte aggregation, a response that could, however, be enhanced by synergistic effects of these concentrations with other contaminants or with physicochemical factors in the field. The alteration of spontaneous hemocyte aggregation is thought to reflect an impairment of hemocyte functions in homeostasis keeping and even in internal defense. This simple assay may constitute an additional tool to experiment the toxic effects of xenobiotics in molluscs.

Toads of the genus Bufo are highly resistant to the toxic effects of digitalis glycosides, and the Na⁺,K⁺-ATPase of all toad tissues studied to date has been relatively insensitive to inhibition by digitalis and related compounds. In studies of brain microsomal preparations from two toad species, Bufo marinus and Bufo viridis, inhibition of ATPase activity and displacement of [³H]ouabain from Na⁺,K⁺-ATPase occurred over broad ranges of ouabain or bufalin concentrations, consistent with the possibility that more than one Na⁺,K⁺-ATPase isoform may be present in toad brain. The data could be fitted to one- or two-site models, both of which were consistent with the presence of Na⁺,K⁺-ATPase activity with high sensitivity to ouabain and bufalin. Ki concentration capable of producing 50% inhibition of activity) values for ouabain in the one-site model were in the 0.2 to 3.7 μM range, whereas Ki₁ values in the two-site model ranged from 0.085 to 0.85 μM, indicating that brain ATPase was at least three orders of magnitude more sensitive to ouabain than B. marinus bladder ATPase (Ki = 5940 μM). Ouabain was also an effective inhibitor of ⁸⁶Rb⁺ uptake in B. marinus brain tissue slices (Ki = 3.1 μM in the one-site model; Ki₁ = 0.03 μM in the two-site model). However, the relative contribution of the high ouabain-sensivity site to the total activity was 17% in the transport assay as compared with 63% in the Na⁺,K⁺-ATPase enzymatic assay. We conclude that a highly ouabain-sensitive Na⁺,K⁺-ATPase activity is present and functional in toad brain but that its function may be partially inhibited in vivo.

Thermophilic microorganisms have been of great scientific interest for several decades, principally in regard to their biotechnological potential and also of the thermostable enzymes they produce. Optimal cultivation techniques for these organisms are required, therefore, not only for basic study but also for evaluation of their thermostable microbial products. Operating a fermentor at elevated temperatures may be advantageous in terms of increased solubility of substrates, improved mass transfer due to decreased viscosity, and increased diffusion rates. However, the cultivation of thermophiles also has many associated problems. A high cultivation temperature can give unexpected problems affecting the choice of reactor design and construction materials, and with the heating and cooling of the fermentor. Other problems may be caused by the low solubility of gases and the instability of substrates and other reagents used. Furthermore, high productivity requires high cell densities to be achieved and in many cases thermophiles are characterised by low growth rates, low growth yields and susceptibility to substrate and product inhibition at low concentrations. Different ways to circumvent some of these problems, such as using gas-lift fermentors, dialysis fermentors or cultivation with cell recycling are discussed.

Glucocorticoids, secreted in response to perceived stress, can suppress immunoglobulin (Ig) levels and compromise immune function in mice and rats. Prairie voles (Microtus ochrogaster) have been reported to exhibit basal corticosterone concentrations that would cause pathological changes in the immune function of most other rodents. The goals of the present study were to verify that serum corticosterone concentration are high in prairie voles, as compared with house mice (Mus musculus), by measuring serum corticosterone with the same RIA; to examine the effects of mild stressors on corticosterone response in both species and to examine the effects of elevated corticosterone levels on IgM and IgG levels in prairie voles and house mice. After 2 weeks of randomly timed 15-min daily restraint or cold-water swim sessions, animals were injected with sheep red blood cells. The data confirmed that basal blood concentrations of corticosterone were higher in prairie voles than house mice, but these high levels doubled after the first swim session in prairie voles, indicating that the adrenals can respond to stressors by producing increased corticosterone. After stress, antibody production (both IgM and IgG) was reduced in house mice but not in prairie voles, despite higher blood concentrations of glucocorticoids in prairie voles. Although body mass was statistically equivalent between species, prairie voles and mice differed dramatically in adrenal and splenic masses. Average adrenal mass of prairie voles was approximately three times the average mass of these organs in house mice; in contrast, the average splenic mass of house mice was approximately three times that of prairie voles. These data may be relevant to seasonal changes in immune function and survival.