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161.
E.A. Shoubridge F.M.H. Jeffry J.M. Keogh G.K. Radda A.-M.L. Seymour 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1985,847(1):25-32
Rats were fed a diet containing 1% of the creatine substrate analogue β-guanidinopropionic acid for 6–10 weeks. 31P-NMR investigation of isolated, glucose-perfused working hearts showed a 90% reduction in [phosphocreatine] from 22.2 to 2.5 μmol/g dry wt in guanidinopropionic acid-fed animals but no change in [Pi], [ATP], or intracellular pH. The unidirectional exchange flux in the creatine kinase reaction (direction phosphocreatine → ATP) was measured by saturation transfer NMR in hearts working against a perfusion pressure of 70 cm of water. This exchange was 10 μmol/g dry wt per s in control hearts and decreased 4-fold to 2.5–2.8 μmol/g dry wt per s in hearts from guanidinopropionic acid-fed animals. Oxygen consumption and cardiac performance were measured in parallel experiments at two perfusion pressures, 70 and 140 cm. No significant differences were observed in oxygen uptake or in any of the performance criteria between hearts from control and guanidinopropionic acid-fed rats at either workload. Assuming an ADP:O ratio of 3, the oxygen consumption measurements correspond to ATP turnover rates of 4.2–7.8 μmol/g dry per s. These rates are 1.5–3-times greater than the rate of the phosphocreatine → ATP exchange in hearts from guanidinopropionic acid-fed rats. These data suggest that phosphocreatine cannot be an obligate intermediate of energy transduction in the heart. 相似文献
162.
Will Edwards Jamie Seymour Katie Pritchard Paul Brock 《Australian Journal of Entomology》2005,44(4):364-368
Abstract In this study we report the results from the first long-term (40 weeks) study of stick-insect fecundity and distribution under natural conditions of which we are aware. We used the number of eggs falling into 72 × 0.5 m2 traps to ask: 'Was egg production in Sipyloidea sp. uniform across the sample period'? and 'Was there evidence of host plant species preference or avoidance'? We collected a total of 213 Sipyloidea sp. eggs. The number of eggs caught per week was not uniform and an exponential decay model was the best-fit relationship between egg production and time, indicative of a steep decline from high to low (but continuous) egg production across the study period. Continuous egg production differs from other insect species in tropical areas that often show distinct seasonal differences between wet and dry seasons, timed to leaf production in host plants. The distribution of eggs within traps was aggregated, and more traps than expected from Poisson probabilities received no eggs, or six or more eggs. The concentration of eggs within particular traps was not related to the identity of canopy plant species, however. We suggest that continuous egg production in Sipyloidea sp. may be related to the wider range of plant species available as food resources for the polyphagous Sipyloidea , compared with other tropical insect species. 相似文献
163.
164.
Robert E. Garrison Seymour O. Schlanger Daniel Wachs 《Palaeogeography, Palaeoclimatology, Palaeoecology》1975,17(1):49-64
The tertiary stratigraphic column on the island of Guam, in the Mariana Island Arc of the western Pacific, is composed largely of volcanic rocks and limestones of shallow-water reef and bank facies. Small amounts of fine-grained limestones, of Eocene, Oligocene and Miocene age, occur interbedded with the volcanic rocks and reef limestones, and consist chiefly of planktonic foraminiferal tests embedded in a matrix of calcareous nannofossils. Although compositionally these pelagic carbonates are nearly identical to nannoplankton-foraminiferal oozes of the deep-sea floor, their deposition probably occurred at comparatively shallow depths — from a few hundred to perhaps 1000–2000 meters rather than several kilometers. The most favorable paleogeographic settings for pelagic deposition of this kind were probably intra-arc basins and shelf areas within the paleo-Mariana Island Arc during periods of volcanic inactivity. The spatial association of these pelagic limestones with shallow-water reef complexes, or with beds of redeposited, reef-derived coarse skeletal material, may serve to differentiate them from their deep-sea counterparts. 相似文献
165.
The relationship between accumulation of cyclic AMP and the secretion of α-amylase was investigated in the rat pancreas . Theophylline and secretin induced an increase in tissue cyclic AMP levels, however, only secretin stimulated secretion of α-amylase. Pancreozymin caused a release of α-amylase and had a biphasic effect on nucleotide levels — stimulation followed by inhibition. Carbachol, which induced a secretory response in the rat pancreas, reduced tissue levels of the cyclic nucleotide. 相似文献
166.
AUTORADIOGRAPHIC LOCALIZATION OF NEW RNA SYNTHESIS IN HYPERTROPHYING SKELETAL MUSCLE 总被引:2,自引:0,他引:2 下载免费PDF全文
Work-induced growth of rat soleus muscle is accompanied by an early increase in new RNA synthesis. To determine the cell type(s) responsible for the increased RNA synthesis, we compared light autoradiographs of control and hypertrophying muscles from rats injected with tritiated uridine 12, 24, and 48 h after inducing hypertrophy. There was an increased number of silver grains over autoradiographs of hypertrophied muscle. This increase occurred over connective tissue cells; there was no increase in the number of silver grains over the muscle fibers. Quantitative studies demonstrated that between 70 and 80% of the radioactivity in the muscle that survived fixation and washing was in RNA. Pretreatment of the animals with actinomycin D reduced in parallel both the radioactivity in RNA and the number of silver grains over autoradiographs. Proliferation of the connective tissue in hypertrophying muscle was evident in light micrographs, and electron micrographs identified the proliferating cells as enlarged fibroblasts and macrophages; the connective tissue cells remained after hypertrophy was completed. Thus, proliferating connective tissue cells are the major site of the increase in new RNA synthesis during acute work-induced growth of skeletal muscle. It is suggested that in the analysis of physiological adaptations of muscle, the connective tissue cells deserve consideration as a site of significant molecular activity. 相似文献
167.
Isolation and characterization of a protease inhibitor from commercial stem bromelain acetone powder
Seven closely related protease inhibitors were isolated from commercial bromelain acetone powder in electrophoretically pure form by gel filtration on Sephadex G-75, followed by ion exchange chromatography on DEAE Sephadex at pH 7.55. The inhibitors are proteins of MW 5000-6000, which inhibit competitively the bromelaincatalyzed hydrolysis of CLN (Ki ≈ 10?7 M). This inhibition is optimal at pH 3 to 4,. and it depends upon the ionization of two acidic residues of pK = 4.5 and 5.0. In the acidic pH range the inhibitors are also effective toward papain, ficin and trypsin. 相似文献
168.
Anesthetized beagle dogs received increasing doses of continuous infusions of a 26-amino-acid synthetic atrial natriuretic factor (ANF). Urinary sodium excretion rose in a dose-dependent manner to a maximum level similar to that seen after hydrochlorothiazide administration. Mean arterial blood pressure decreased, but only modestly, and not in a dose-dependent fashion. Dogs chronically retaining NaCl secondary to constriction of the thoracic inferior vena cava showed only modestly enhanced natriuresis when infused with similar levels of ANF. When ANF was infused directly into the renal artery of anesthetized beagles, a dose-dependent natriuresis and calciuresis were observed with maximal fractional sodium excretion averaging approximately 8%. Although glomerular filtration tended to increase, the average dose-related changes were not significant. Cyclic GMP excretion was increased during intra-renal-arterial infusion of ANF. Excretion of cyclic GMP by both the infused and noninfused kidneys was equal, which suggests that urinary cyclic GMP was not nephrogenous but derived from the elevated circulating levels. These and other data from rats dissociate changes in urinary cyclic GMP excretion and sodium excretion. 相似文献
169.
The effect on the recovery of mechanical function, ATP, phosphocreatine, Pi and pH of various lengths of total global ischaemia in the insulin-treated, perfused rat heart has been studied using 31P-NMR. Insulin-treated hearts recovered stable mechanical function after 18 min ischaemia when their intracellular pH was 6.0 and 70% of the pre-ischaemic ATP remained. Hearts perfused without insulin fail to recover after 18 min ischaemia, having an intracellular pH of 6.3 and 40% of ATP remaining (Bailey, I.A., Seymour, A.-M.L. and Radda, G.K. (1981) Biochim, Biophys. Acta 637, 1-7). Thus, ATP maintenance in ischaemia is more important to recovery on reperfusion than is maintaining intracellular pH. The importance of this observation in devising biochemical strategies for the clinical protection of the myocardium is discussed. 相似文献
170.