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31.
Summary Quantitative electron microprobe analysis was employed to compare the effects of aldosterone and ADH on the intracellular electrolyte concentrations in the toad urinary bladder epithelium. The measurements were performed on thin freeze-dried cryosections utilizing energy dispersive x-ray microanalysis. After aldosterone, a statistically significant increase in the intracellular Na concentration was detectable in 8 out of 9 experiments. The mean Na concentration of granular cells increased from 8.9±1.3 to 13.2±2.2 mmol/kg wet wt. A significantly larger Na increase was observed after an equivalent stimulation of transepithelial Na transport by ADH. On average, the Na concentration in granular cells increased from 12.0±2.3 to 31.4±9.3 mmol/kg wet wt (5 experiments). We conclude from these results that aldosterone, in addition to its stimulatory effect on the apical Na influx, also exerts a stimulatory effect on the Na pump. Based on a significant reduction in the Cl concentration of granular cells, we discuss the possibility that the stimulation of the pump is mediated by an aldosterone-induced alkalinization.Similar though less pronounced concentration changes were observed in basal cells, suggesting that this cell type also participates in transepithelial Na transport. Measurements in mitochondria-rich cells provided no consistent results. 相似文献
32.
图论在中国慈姑属数量分类研究中的应用 总被引:1,自引:0,他引:1
.黄德世;.钟扬;.陈家宽 《武汉植物学研究》1988,6(4):405-406
慈姑属(Sagittaria L.)是水生单子叶植物泽泻科(Alismataceae)的一个重要属。近年来,陈家宽等对中国慈姑属进行了系统研究。作者应用聚类分析和主成分分析进行了中国慈姑属的数量分类,取得了良好的效果。由于慈姑属分类性状数目较大,因而在压缩后的三维空间中描述分类群间的距离, 相似文献
33.
In our previous study vesamicol, an inhibitor of the acetylcholine transporter of the cholinergic vesicles, inhibited veratridine-evoked external Ca2+-dependent acetylcholine release from striatal slices but did not influence acetylcholine release observed in Ca2+-free medium (4). Here we examined if the effect of veratridine on membrane potential, Ca2+ uptake, and intracellular Ca2+ concentration of synaptosomes was altered by vesamicol in parallel with the inhibition of acetylcholine release. The depolarizing effect of 10 M veratridine (from 67±2.3 mV resting membrane potential to 50.7±2.5 mV) was not significantly influenced by vesamicol (1–20 M). Vesamicol (1–20 M) had no effect on either the overall curve of the veratridine-evoked45Ca2+ uptake or the amount of Ca2+ taken up by synaptosomes. Veratridine caused a rise in intrasynaptosomal Ca2+ concentration as measured by Fura2 fluorescence, and the same increase both in characteristics and in magnitude was observed in the presence of vesamicol (20 M). The K+-evoked (40 mM) increase of Ca2+ uptake and of intracellular calcium concentration were also unaltered by vesamicol. In high concentration (50 M) vesamicol inhibited both the fall in membrane potential and the elevated Ca2+ uptake by veratridine, indicating a possible nonspecific effect on potential-dependent Na+ channels at this concentration. Vesamicol, in lower concentration (20 M) when neither of the above parameters was changed, completely prevented veratridine-evoked increase of [14C]acetylcholine release. This was observed only when vesamicol was present in the media throughout the experiment after loading the preparation with [14C]choline. The results suggest that vesamicol does not interfere with veratridine-induced changes in isolated nerve terminals other than with the release of acetylcholine, thus further supporting the involvement of a vesamicol-sensitive vesicular transmitter pool in Ca2+-dependent veratridine-elicited acetylcholine release. 相似文献
34.
A continuous-culture approach to the question of inorganic carbon concentration by Synechococcus species 总被引:1,自引:0,他引:1
Abstract Chemostat cultures of Synechococcus PCC7942 were established in steady state over ten generations with inorganic carbon-limiting biomass production. The bicarbonate-concentration process was not significantly induced; RuBisCo activity was increased six-fold with decreasing dissolved inorganic carbon concentration and the presence of the 42-kDa cytoplasmic membrane polypeptide was observed but not implicated in the process. 相似文献
35.
36.
A field experiment was conducted for five consecutive years to determine upland rice (Oryza sativa L.) and common bean (Phaseolus vulgaris L.) response to eight P sources at three P rates in an Oxisol of Central Brazil. The P sources tested were triple superphosphate
(TSP), Arafertil phosphate partially acidulated (APPA), phosphate of Patos partially acidulated (PPPA), phosphate of Araxa
concentrated (PAC), phosphate of Catalao (PC), phosphate of Jacupiranga (PJ), phosphate of Patos de Minas (PPM), and phosphate
of Abaete (PA). All phosphate rock sources were of Brazilian origin. The P rates used were 87, 174 and 262 kg P ha-1. Yield response to P sources and rates varied from crop to crop. Rice and bean yields were significantly correlated with
Bray 1 P, but not Mehlich 1 P. In the first year, TSP and the two partially acidulated phosphate rocks (APPA, PPPA) produced
higher grain yields. In the second year and all remaining years of the experiment, the efficiency of phosphate rock sources
as measured by grain yield was equivalent to TSP or partially acidulated P sources. The results suggest that these phosphate
rock sources could be used in rice-bean rotations on Brazilian Oxisols. Yield losses in the first year could be partially
offset by the addition of a small amount of soluble P. 相似文献
37.
Temporal changes in tissue glutathione in response to chemical form,dose, and duration of selenium treatment 总被引:1,自引:0,他引:1
Selenium has been reported to affect glutathione (GSH) concentrations in short-term animal-feeding experiments. Given the central role that this tripeptide plays in maintaining cellular homeostasis, it was hypothesized that perturbations in glutathione metabolism induced by selenium might account for its cancer chemopreventive activity. In the present study, four experiments were conducted in which the effect of acute, short-, or long-term exposure to selenium was assessed. Selenium was provided as either sodium selenite or D,L-selenomethionine. Selenite was observed to induce a biphasic response in total liver GSH. Injected selenium caused an acute reduction in GSH, whereas short-term feeding (up to 8 wk) increased both total GSH and oxidized glutathione (GSSH), an effect that gradually diminished in magnitude with prolonged feeding. Our data suggest that such changes are unlikely to account for the chemopreventive activity of selenium for the following reasons: Perturbations in glutathione metabolism occurred only at doses of selenite that approached toxicity. These doses are higher than what would be required for producing cancer chemoprevention. The transient nature of these changes also contrasts with the need for a continuous supplementation of selenite in suppression of tumorigenesis. Furthermore, selenomethionine was found to have little activity in altering glutathione metabolism, even though it compares favorably with selenite as a cancer chemopreventive agent. Nonetheless, these findings do not discount the possibility that sulfhydryl compounds, such as glutathione, might be used to modify the toxicity and/or enhance the cancer prophylactic activity of selenium compounds. 相似文献
38.
The energy status of mammalian cells is a finely regulated phenomenon. This is especially true in cardiac muscle cells in which energy requirements are high and the system must provide rapid turnover of the adenine nucleotides and instant response to changes in energetic demands. We have examined the acute response of the rat myocardium to ventricular pacing up to 2.5 times the resting heart rate. The purpose of this study was to determine at what level of pacing the normal energy status could be maintained and at what point it was compromised. Myocardial energy charge (EC = (ATP + 0.5 ADP)/(ATP + ADP + AMP)) was maintained at 1, 1.5 and 2 times the resting heart rate but declined significantly at 2.5 times. In contrast, phosphorylation potential (PP = ATP/ADP1 × Pi) was drastically altered in hearts paced at 1.5, 2 and 2.5 times the resting rate. Tissue lactate increased and glycogen decreased in a linear fashion as pacing rate increased, indicating that the metabolic challenge was proportional to the pacing rate. EC seems to reflect the overall status of the cell and its ability to maintain a dynamic equilibrium. PP may reflect the immediate and necessary driving force for mitochondrial respiration in times of increased demand. These data suggest that the myocardium may meet the increased energy demands of acute ventricular pacing by shifting the molar ratio of ATP to ADP times Pi in favour of driving phosphorylation. 相似文献
39.
In rat hippocampal slices GABAergic IPSPs are very rapidly suppressed by anoxia (in<2 min). Both early (GABAA) and late (GABAB) components are affected. After reoxygenation, the IPSPs recover, but only slowly and not always completely. Iontophoretic applications of GABA or baclofen indicated no major depression of responses during anoxia. It is therefore unlikely that the anoxic suppression of IPSPs is caused by desensitizations of GABA receptors. A more probable explanation is a failure of GABAergic neurons to release GABA from inhibitory nerve terminals.Special issue dedicated to Dr. Eugene Roberts. 相似文献
40.
James V. Moroney N. E. Tolbert Barbara B. Sears 《Molecular & general genetics : MGG》1986,204(2):199-203
Summary Six independently isolated mutants of Chlamydomonas reinhardtii that require elevated CO2 for photoautotrophic growth were tested by complementation analysis. These mutants are likely to be defective in some aspect of the algal concentrating mechanism for inorganic carbon as they exhibit CO2 fixation and inorganic carbon accumulation properties different from the wild-type. Four of the six mutants defined a single complementation group and appear to be defective in an intracellular carbonic anhydrase. The other two mutations represent two additional complementation groups.Abbreviations HS
high salt medium which has 13 mM phosphate at pH 6.8
- HSA
high salt plus 36 mM acetate medium
- YA
high salt medium with 4 g yeast extract per L and 36mM acetate
- Arg
arginine
- cia-
CO2 accumulation mutants that cannot grow on low CO2
- Ci
inorganic carbon (CO2+HCO
-
3
)
- CA
carbonic anhydrase
- mt
mating type
Supported in part by the McKnight Foundation and by NSF grant PCM 8005917 and published as journal article 11924 from the Michigan State Agriculatural Experiment Station 相似文献