Comparative Biochemistry and Physiology Part A: Physiology最新文献

Antarctic fish of the family Channichthyidae, or icefish, represent a unique model for the study of physiological and biochemical responses to chronic hypoxia since the genes coding for hemoglobin and possible myoglobin are not expressed by these teleosts. Channichthyidae have developed outstanding cardio-vascular adaptations to accommodate the lack of these hemic pigments, most of them involving the myocardium.

Different binding activities of ¹²⁵I-rat atrial natriuretic peptide were evaluated using in vitro quantitative autoradiography in the heart of two antarctic notothenioid teleosts, the red-blooded Trematomus bernacchii and hemoglobinless Chionodraco hamatus. Saturable and specific binding sites for rat atrial natriuretic peptide were found in the atrium, ventricular myocardium, ventricular endocardium and inner and outer layers of the bulbus arteriosus of both fishes. Scatchard analysis of the saturation data showed that the atrium, ventricular endocardium and outer bulbar layer of T. bernacchii were characterized by a single class of high affinity natriuretic peptide binding sites (K_d = 14 ± 3.2, 9.7 ± 2.3 and 6.2 ± 1.3 pM, respectively), whereas the ventricular myocardium and the inner bulbar layer contained elevated numbers of two classes of high and low affinity natriuretic peptide binding sites (1.8 ± 0.6 < K_d < 209 ± 66 pM). In contrast, in C. hamatus, both high and low affinity binding sites were detected in all cardiac regions (2.1 ± 0.7 < K_d < 262 ± 90 pM). In both fishes, competition experiments in the presence of either unlabeled rat atrial natriuretic peptide or porcine brain natriuretic peptide indicated different displacement capacities. Porcine brain natriuretic peptide, able to bind to natriuretic peptides sites in all the heart regions of both notothenioids, provided a higher displacement capacity with respect to that of rat atrial natriuretic peptide in the atrium of T. bernacchii.

The superficial extensor muscles of the crayfish abdomen were examined as a possible site for modulation by DF₂ (Asp-Arg-Asn-Phe-Leu-Arg-Phe-NH₂), a FMRFamide-related neuropeptide found in crayfish pericardial organs (26). The superficial extensor muscles are of the tonic type and generate slow contractions that affect posture. DF₂, at concentrations of 10⁻⁸ M or higher, increased muscle tonus in isolated, unstimulated neuromuscular preparations. In some preparations, the peptide also induced small, arrhythmic contractions or increased the amplitude of such contractions if they were already present. The spontaneous contractions were temperature-dependent and insensitive to 10⁻⁷ M tetrodotoxin, indicating that they were myogenic. DF₂ increased muscle tonus in the presence of tetrodotoxin and when nerve-evoked contractions were blocked using Joro spider toxin (JSTX), a glutamate receptor antagonist. Thus, the effects of DF₂ on contraction appear to represent direct effects on the muscle and not changes in release of chemical transmitter from nerve terminals. DF₂ did not alter resting membrane potential or input resistance in the muscle fibres.

The effects of DF₂ on contraction were blocked by the Ca²⁺ channel antagonists Mn²⁺ Ni²⁺ and Cd²⁺ and nicardipine, and by replacing extracellular Ca²⁺ with Mg²⁺. This suggests that the peptide's effect may require an influx of extracellular Ca²⁺ through dihydropyridine-sensitive Ca²⁺ channels. The Ca²⁺ channel antagonists also reduced muscle tonus on their own, suggesting that they may lower the intracellular calcium concentration. The peptide might act by enhancing Ca²⁺ influx or by enhancing Ca²⁺-dependent release of Ca²⁺ ions from internal stores.

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.

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.

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.

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.