鲢、鳙在天然条件下的摄食强度(Ⅱ)武汉东湖鲢、鳙周年摄食强度的研究

武汉东湖的鲢(Hypophthalmichthy molitrix)鳙(Aristichthys nobilis)在天然条件下摄食强度具季节性变化。摄食强度高峰处于夏季,低谷处于冬季。在实验条件下,按周年采样期间水温变化范围,测定鱼的肠管排空率。食物通过鱼肠管时间(Y_p—h)与水温(X_t—℃)的关系为: 鲢Y_p=270.63 X_t~(0.6408) 鳙Y_p=280.46 X_t~(0.6642) 根据修正后Bajkov公式(D=C (24.A)/n),估算鱼的日粮。鱼日粮(Y_D)与水温(X_t)关系为: 鲢Y_D=0.2683e~(0.1503X_t) 鳙Y_D=0.0075X_t~(2.2715) 计算鱼在天然条件下周年月粮及年粮。鲢、鳙对天然饵料年消耗量分别为18.924公斤及17.39公斤,饵料系数分别为18.02及13.38。     

Hydroxyl radical production during oxidative deposition of iron in ferritin

The chemistry of oxidative deposition of iron(III) in ferritin and apoferritin is poorly understood. This study was undertaken to look for radicals formed as the hydrous ferric oxide core is developed from Fe(II) and O2. Radicals were observed indirectly by using the spin-trapping reagent N-tert-butyl-alpha-phenylnitrone (PBN) at room temperature and directly by measuring ESR spectra of frozen solutions at 77 K. In both instances, radical production was inhibited by the hydroxyl radical scavenging agents dimethyl sulfoxide, thiourea, and mannitol and enhanced by the addition of hydrogen peroxide. These findings strongly suggest that hydroxyl radical, produced from the iron-catalyzed Haber-Weiss reaction, is a by-product of core formation in ferritin and is a precursor to the observed radicals. The yield of ESR-observable and spin-trapped radicals is quite low, being at the micromolar level when millimolar concentrations of ferrous ion are employed. Furthermore, radical production appears to be confined to the interior of the ferritin molecule, where cellular components would be protected from the oxygen-derived toxic effects of iron. It is postulated that hydroxyl radical-medicated oxidative damage to the protein, a process that may contribute to the formation of hemosiderin from ferritin, leads to the observed radicals. By serving as a sink for hydroxyl radical, the protein shell may therefore efficiently minimize damage to other biomolecules in the cell.     

Construction of the endoplasmic reticulum

To study the construction of the ER, we used the microtubule-disrupting drug nocodazole to induce the complete breakdown of ER structure in living cells followed by recovery in drug-free medium, which regenerates the ER network within 15 min. Using the fluorescent dye 3,3'-dihexyloxacarbocyanine iodide to visualize the ER, we have directly observed the network construction process in living cells. In these experiments, the ER network was constructed through an iterative process of extension, branching, and intersection of new ER tubules driven by the ER motility previously described as tubule branching. We have tested the cytoskeletal requirements of this process. We find that newly formed ER tubules are aligned with single microtubules but not actin fibers or vimentin intermediate filaments. Microtubule polymerization preceded the extension of ER tubules and, in experiments with a variety of different drugs, appeared to be a necessary condition for the ER network formation. Furthermore, perturbations of the pattern of microtubule polymerization with microtubule-specific drugs caused exactly correlated perturbations of the pattern of ER construction. Induction of abnormally short, nonintersecting microtubules with 20 microM taxol prevented the ER network formation; ER tubules only extended along the few microtubules contacting the aggregated ER membranes. This requirement for a continuous network of intersecting microtubules indicates that ER network formation takes place through the branching and movement of ER membranes along microtubules. Cytochalasin B had no apparent effect on the construction of the ER network during recovery, despite apparently complete disruption of actin fibers as stained by phalloidin. Blockage of protein synthesis and disorganization of intermediate filaments with cycloheximide pretreatment also failed to perturb ER construction.     

Age determination in the adult screwworm (Diptera: Calliphoridae) by pteridine levels

Fluorescence spectrophotometry was used to assess the possible use of pteridines in the compound eyes to estimate the age of adult screwworms, Cochliomyia hominivorax (Coquerel). Factors affecting the quantities of pteridines include temperature and head size. No difference in pteridine levels was found among flies fed protein or carbohydrate. A regression model for estimating the age of female screwworms was constructed. The model uses head capsule size and relative pteridine quantities and assumes a constant body temperature of 30 degrees C. This regression formula has an r2 of 0.74. Our study extends the use of pteridine accumulation for age determination from obligate sanguinivorous Diptera to an autogenous species that feeds facultatively on nectar and wound exudates. The technique appears to provide a valid means to determine age of these flies.     

Molecular characterization of a major autoantibody-associated cross-reactive idiotype in Sjogren's syndrome

Primary Sjogren's syndrome is an autoimmune disorder characterized by lymphocytic infiltration of the salivary and lacrimal glands, producing associated dry eyes (keratoconjunctivitis sicca), dry mouth, and intermittently swollen salivary glands. A high proportion of the infiltrating B lymphocytes express surface and cytoplasmic Ig bearing a kappa-L chain-associated CRI defined by reactivity with the murine mAb, 17.109. To determine the structural basis for CRI expression in this disease, we generated CRI+ lymphoblastoid cell lines and a cDNA library from lymphocytes extracted from Sjogren's syndrome patients' salivary gland biopsy specimens. Nucleic acid sequence analyses of the mRNA of one such 17.109-CRI+ lymphoblastoid cell line (NOV) reveals the expressed kappa light chain variable region gene (V kappa gene) to be homologous to Humkv325, a conserved V kappa gene used at relatively high frequency in certain B cell malignancies. In addition, synthetic oligonucleotides, corresponding to the first and third frameworks and the second complementarity determining region of the Humkv325 gene, were used to identify and isolate clones from a cDNA library generated from SS salivary gland lymphocytes. Clones annealing specifically with one or more of these oligonucleotide probes contained kappa light chain cDNA. The sequences corresponding to the variable region of two clones (Taykv320 and Taykv306) were homologous to Humkv325. The V kappa genes of four other cDNA clones (Taykv322, Taykv310, Taykv308, and Taykv312) most likely were generated somatically from the rearranged Humkv325 gene through a limited number of nucleic acid base substitutions. Our results suggest that the high frequency of 17.109-CRI expression in Sjogren's syndrome patients results from a multiclonal expansion of B cells using Humkv325, and that the expressed Humkv325 may undergo somatic diversification in an apparent Ag-driven response.     

Sodium and calcium currents in action potentials of rat somatotrophs: their possible functions in growth hormone secretion

We report that both Na+ and Ca2+ currents are involved in the action potentials and in the hormone release from rat somatotrophs in primary culture. Single somatotrophs were identified by reverse hemolytic plaque assay (RHPA) and transmembrane voltage and currents were recorded using the whole-cell mode of the patch-clamp technique. Somatotrophs displayed a mean resting potential of -80mV and an average input resistance of 5.7G omega. Most of the cells showed spontaneous or evoked action potentials. Single action potentials or the initial spike in a burst were characterized by their high amplitude and short duration. Tetrodotoxin (TTX, 1 microM) blocked single action potentials and the initial spikes in a burst, whereas action potentials of long duration and low amplitude persisted. Cobalt (2 mM) plus TTX (1 microM) blocked all the action potentials. Voltage-clamp experiments confirmed the presence of both a TTX-sensitive Na+ current and Co2(+)-sensitive Ca2+ currents. TTX or Na(+)-free medium slightly decreased the basal release of GH but did not markedly modify hGRF-stimulated GH release. However, Co2+ (2 mM), which partially decreased the basal release, totally blocked hGRF-stimulated release. We conclude that (1) Na+ currents which initiate rapid action potentials may participate in spontaneous GH release; (2) Ca2+ currents, which give rise to long duration action potentials and membrane voltage fluctuation, are probably involved in both basal and hGRF-stimulated GH releases.     

HIV-1 entry into quiescent primary lymphocytes: molecular analysis reveals a labile, latent viral structure

Productive infection of human T lymphocytes by HIV-1 is dependent upon proliferation of the infected cell. Nonproliferating quiescent T cells can be infected by HIV-1 and harbor the virus in an inactive state until subsequent mitogenic stimulation. We use a modification of the polymerase chain reaction method, which is both sensitive and quantitative, to demonstrate that HIV-1 DNA synthesis is initiated in infected quiescent T cells at levels comparable with those of activated T cells. However, unlike that of activated T cells, the viral genome is not completely reverse transcribed in quiescent cells. Although this viral DNA structure can persist in quiescent cells as a latent form, it is labile. We discuss the lability of this HIV-1 DNA structure in relation to a "self-restricting persistent infection" by HIV-1 and propose that this may explain the low percentage of infected cells in the circulation of AIDS patients.     

3H]L-657,743 (MK-912): a new, high affinity, selective radioligand for brain alpha 2-adrenoceptors

L-657,743 (MK-912), a highly potent and selective alpha 2-adrenoceptor antagonist was tritiated to a high specific activity and its binding characteristics to brain tissue were determined. The specific binding of [3H]L-657,743 to rat cerebrocortex was saturable, reversible, and dependent on tissue concentration. In saturation studies, [3H]L-657,743 binding was resolved into two high affinity components exhibiting Kd values of 86 pM and 830 pM with densities of 82 fmol/mg protein and 660 fmol/mg protein, respectively. Based on the binding potencies of a variety of compounds with differing receptor selectivities, the sites labeled by [3H]L-657,743 were characteristic of alpha 2-adrenoceptors. In contrast to alpha 2-antagonists, alpha 2-agonists displayed shallow competition curves. In the presence of 100 microM GTP, Gpp(NH)p or 150 mM NaCl, the competition curve for epinephrine was shifted to the right, whereas that for yohimbine was unaffected. In studies utilizing human cerebrocortical tissue, [3H]L-657,743 also bound with high affinity to sites characteristic of alpha 2-adrenoceptors.