Effects of dexamethasone on carnitine metabolism in liver and extrahepatic tissues

The in vivo effects of dexamethasone administration on liver and extrahepatic tissue carnitine concentrations were assessed in 48-h-starved rats. In heart and kidney, but not in liver, dexamethasone significantly increased total carnitine concentration. Acute (2.5 h) treatment with 2-tetradecylglycidate (TDG), a specific inhibitor of carnitine palmitoyl transferase 1, not only increased total hepatic carnitine concentrations, but also permitted an effect of dexamethasone (a further increase in hepatic carnitine concentration). The results are discussed in terms of acute (substrate-mediated) and chronic (hormonal) control of carnitine turnover.     

The effect of substrate modification on binding of porcine pancreatic alpha amylase: hydrolysis of modified amylose containing D-allose residues

A modified amylose containing 10% of tritiated D-allose residues has been hydrolyzed by porcine pancreatic alpha amylase (PPA). This reaction produced a number of radioactive oligosaccharides of low molecular weight, including modified mono-, di-, and tri-saccharides, as well as larger products. Analysis of these products by chemical and enzymic methods identified D-allose, two isomers of modified maltose, and isomers of modified maltotriose. These results may be interpreted in terms of current PPA models to indicate that D-allose residues may be productively bound at all five subsites of the active site of the enzyme. The distribution of modified residues in these products, however, further suggests that productive binding of D-allose at the subsite where catalytic attack occurs (subsite 3) is less favorable than binding of D-glucose. These results are compared with results of a series of PPA substrates having modifications at C-3 and at other positions. Trends observed in enzyme hydrolysis of these modified substrates reflect factors that contribute to PPA catalysis, with respect to steric, electronic, and hydrogen-bonding interactions between enzyme and substrate.     

Seasonal changes in density and tissue distribution of Onchocerca cervicalis microfilariae in ponies and related changes in Culicoides variipennis populations in Louisiana

Seasonal changes in density and spatial distribution of Onchocerca cervicalis microfilariae were studied in ventral-midline skin of 15 infected pony mares in southern Louisiana. Triple running mean analysis of data over a 13-mo period indicated that a distinct pattern exists in total microfilariae population density and in microfilariae occurrence in different levels of the dermis. Microfilariae density reaches peak levels in the spring followed by a 58% decrease in the summer, a 19% increase in the fall, and a decrease to the lowest numbers in the winter. Microfilariae were found in all levels of the skin during the spring, summer, and fall but were not found in the superficial layers of the dermis during the winter months. The population density of Culicoides variipennis, a demonstrated vector of O. cervicalis, appeared to have seasonal fluctuations similar to the changes in microfilarial density. Harmonic wave analysis of microfilariae density data in individual ponies showed that all individuals did not follow the population trend.     

Primary structure and androgen regulation of a 20-kilodalton protein specific to rat ventral prostate

Nuclear and cytosolic forms of a 20-kdalton rat ventral prostate protein were purified and partially sequenced from their N-termini. Isolated nuclei were treated with micrococcal nuclease and extracted in 0.6 M NaCl, and proteins were separated by affinity chromatography on Matrex gel green A, ammonium sulfate fractionation, and fast protein liquid chromatography on Superose 12. The 43 amino acid N-terminal sequence of the nuclear 20-kdalton protein was identical with the cytosolic protein except it lacked 7 N-terminal amino acids present in the cytosolic form. The DNA sequence of a full-length complementary DNA clone isolated from a ventral prostate gt11 library extended the N-terminal sequence of the cytosolic form by an additional nine amino acids from the predicted initiation methionine. The cDNA included the nucleotide sequence for the 43 amino acid N-terminal sequence of the purified 20-kdalton protein and predicted molecular weights of 16,686, 17,521, and 18,650, respectively, for the nuclear, cytoplasmic, and nonprocessed proteins. Northern blot analyses of reproductive tract tissue RNAs using the 20-kdalton protein cDNA as probe revealed a single mRNA species of 0.92 kb detectable only in extracts of rat ventral prostate. Expression of the 0.92-kb mRNA was androgen dependent since the mRNA was undetectable in extracts obtained 4 days after castration and was restored 16 h after restimulation with androgen.     

Antibodies to steroid receptor deoxyribonucleic acid binding domains and their reactivity with the human glucocorticoid receptor

Functional properties of the DNA-binding domain of the human glucocorticoid receptor were investigated using high titer polyclonal antibodies produced against single synthetic peptides or a mixture of peptides whose sequences were derived from the DNA-binding domain of steroid receptor proteins. Three of seven antisera recognized both native and denatured forms of the glucocorticoid receptor, although considerably lower antisera dilutions were required for antibody binding to native receptor. Activation of the glucocorticoid receptor to its DNA-binding form was required for antibody recognition of the native receptor. Antisera to the second finger region of the DNA-binding domain caused a portion of the activated 4S glucocorticoid receptor to sediment as 7 or 9S in sucrose gradients containing 0.4 M KCl, but did not alter the sedimentation of the nontransformed 8S receptor. Specificity of the glucocorticoid receptor-antibody interaction was demonstrated by loss of reactivity after preabsorption with peptide antigens. Antisera that interacted specifically with the glucocorticoid receptor inhibited DNA binding of the activated receptor by as much as 80%. Thus, antibody probes directed against DNA-binding domain sequences provide immunological evidence that glucocorticoid receptor activation exposes the DNA-binding region of the receptor.     

Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

A comparison between Northern and Southern Hemisphere tundras and related ecosystems

Summary Climatic, edaphic, and vegetation parameters are compared among three Subantarctic islands and one Maritime Antarctic island, and Northern Hemisphere tundras and tundra-like ecosystems (ranging from higharctic to cool-temperate oceanic and temperate alpine), mainly by Principal Component Analyses (PCA). All analyses of abiotic variables emphasized the extreme oceanicity of the Southern Hemisphere sites and showed the strong influence of seaspray on soil nutrient ratios in the southern sites. Analyses of climate classified all the southern sites as Cold Oceanic within a series of very oceanic climates that were distinct from the continental/subalpine climates more typical of the northern sites. Four factorial groups were derived from the vectors in PCA of soils and climate combined. Each was a grouping of several variables that was essentially independent of the other groups. They were: general climatic severity, soil base status, supply of labile nutrients, and a combined index of oceanicity with organic/mineral balance and drainage. The ecological significance of these is discussed. The range of soil nutrient levels in the southern sites is approximately equal to that of the northern sites; however, in the southern sites soil nutrient levels are inversely related to climatic severity while in the north the reverse is true. The two most important causes of these opposed trends are the relative ages of the sites and the much greater effects of sea-based vertebrates (e.g. seals and seabirds) in the southern islands. Cluster analyses of component scores derived from climatic and soil data linked the southern sites with northern sites at higher latitudes, indicating the effect of the Antarctic continent on the Southern Ocean (hence on the overall climate of the southern islands) and of wind-chill on the aerial and soil climates of the southern sites. Vegetation patterns (derived from PCA of life form data) were more complex because of the serial replacement of one lifeform by onother along continuous environmental gradients. Wind exposure was an important element in the first two vectors derived from the PCA of the botanical data. The Southern Hemisphere sites exhibited almost the full range of vegetation types found in the Northern Hemisphere, despite their floristic poverty. Variation within individual islands was comparable with that found at considerably higher (up to 30° more) northern latitudes and reflects the overriding importance of wind exposure in the southern islands. Subarctic ecosystems are generally less severe forms of Arctic ones, and decreasing latitude leads to increasingly milder environments with no great changes overall in continentality. In contrast, the Subantarctic combines elements from the extremes of the range of northen tundras (i.e. high-Arctic and cool-temperate oceanic) with its own peculiar features (e.g. animal influences) to produce ecosystems that are qualitatively different both from Subarctic systems and from the continental Antarctic regions to which they are geographically closest.     

Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

The effects of microtubule dissociating agents on the physiology and cytology of the sensory neuron in the femoral tactile spine of the cockroach, periplaneta americana L

Microtubules are prominent cellular components of the mechanosensory and chemosensory sensilla associated with the insect cuticle, and a range of hypotheses have been proposed to account for their role in sensory transduction. Chemical agents such as colchicine and vinblastine, which dissociate microtubules, also interfere with transduction in these sensilla, and this has been attributed to their anti-microtubule activity. We have now examined the dynamic properties of sensory transduction in the mechanosensitive neuron of the cockroach femoral tactile spine, after the application of colchicine, vinblastine and lumicolchicine. Concurrently we have examined the ultrastructure of the same sensory ending by transmission electron microscopy. All of the drugs reduced the mechanical sensitivity o the receptor. Colchicine and vinblastine achieved this reduction without altering the dynamic properties of the receptor but lumicolchicine changed the dynamic response, and increased the relative sensitivity to rapid movements. Conduction velocity, another measure of neuronal function, which relies upon ionic currents flowing through the membrane, was reduced by all three drugs. The effects of the drugs upon the ultrastructure of the sensory ending were also disparate. In the case of colchicine there was complete dissociation of microtubules in the tubular body and distal dendrite before a total loss of mechanical sensitivity. Vinblastine was less effective in dissociating microtubules, although more effective in the reduction of mechanical sensitivity. With lumicolchicine the dominant morphological effect was a severe disruption of the dendritic membrane. We conclude from these experiments that microtubules are not essential in the transduction of mechanical stimuli by cuticular receptors and that the effects of these drugs upon mechanosensitivity are not directly related to their dissociation of the microtubules in the tubular body, but are more likely to arise from actions upon the cell membrane. These actions could include effects upon tubulin in the membrane or upon other membrane components.