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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A pH dependent reduction in growth, pigment, ATP content, O2- evolution, carbon fixation, photosynthetic electron transport system, nutrient uptake (NO3- and NH4+), nitrate reductase, and ATPase activities and increase in K+ efflux of Chlorella vulgaris was noticed following supplementation of Cu and Ni to the culture medium. PS II was found to be more sensitive to both pH and metals than PS I. Though, nitrate reductase (NR) was more sensitive to both pH and metals, the ATPase was however, more sensitive to metals but less sensitive to acidic pH. Acid pH was found to inhibit the nutrient (NO3- and NH4+) uptake and nitrate reductase in a non-competitive manner. The inhibition produced by the test metals alone was of non-competitive type for NO3- uptake, nitrate reductase and ATPase and competitive for NH4+ uptake. Acidity not only inhibited the metabolic variables directly but also through facilitated uptake of metals and increased membrane permeability. A very low sensitivity of ATPase to acidic pH seems to be responsible for the survival of algae in acid environment.
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PMID:Effect of Cu and Ni on growth, mineral uptake, photosynthesis and enzyme activities of Chlorella vulgaris at different pH values. 802 20

The purpose of this study was to investigate whether vitamin D3 deficiency affects the cardiac function of chick hearts directly or whether the influence is secondary through the hormone's effect on serum calcium levels. To this end, three experimental groups were studied: (a) the control group of vitamin D3 supplemented chicks, Ds, (b) vitamin D3 deficient chicks, Dd, and (c) vitamin D3 supplemented hypocalcemic chicks raised on decreased calcium levels, Dh. The three groups were compared by checking hemodynamic, metabolic and membrane parameters. Total and ionized serum calcium concentrations in the Dh and Dd groups were found to be lower than in the Ds group. Perfusion of the isolated hearts with solutions containing various calcium concentrations (1, 1.5 and 2.5 mM) induced enhanced contractility levels, the magnitude of which was dependent on the difference between the in vivo and perfusate calcium levels. Thus, the inotropic effect was similar and more enhanced for the two hypocalcemic groups. The differences in hemodynamic behaviour could not be explained by variations in the levels of the high energy compounds and acidity, since similar ATP, creatine phosphate and intracellular pH levels were detected for both Ds and Dd groups. However, membrane studies revealed an increase in the number of slow calcium channels for the two hypocalcemic groups and this may be the possible mechanism for the differences in the contractile activity. In conclusion, our study strongly suggests that the effects of vitamin D3 on the heart is mediated only indirectly through its effect on serum calcium levels.
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PMID:The effect of vitamin D3 deficiency on the isolated chick heart: hemodynamic, P-31 NMR and membrane studies. 838 50

Endosomal proteases have been implicated in the degradation of internalized regulatory peptides involved in the control of metabolic pathways and in the processing of intracellular antigens for cytolytic immune responses. Processing in the endocytic vesicles is regulated by changes in endosomal acidity due to the presence of an ATP-dependent proton pump which modulates protease activity, protein unfolding and receptor-ligand interactions. A limited number of proteases appear to reside in endosomes which do not contain the full complement of active proteases capable of completely degrading all internalized polypeptides. Retention of some acid hydrolases in endosomes is apparently related to their association with undefined endosomal membrane receptors. The limited number of proteases and the pH gradient from neutral to acidic (pH 7 to 5) within endosomes make possible a selective and controlled processing environment in comparison to lysosomes. The full set of endo- and exopeptidases that break down proteins to amino acids are active later in the pathway in lysosomes.
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PMID:Endosomal proteolysis of internalized proteins. 868 6

This study demonstrates a pH-dependent inhibition of Mg(2+)- and Ca(2+)-ATPase activities of Nostoc linckia and Chlorella vulgaris exposed to AlCl3, AlF3, NaF and AlCl3+NaF together. AlF3 and the combination of AlCl3+NaF were more inhibitory to both the enzymes as compared with AlCl3 and NaF. Toxicity of the test compounds increased with increasing acidity. Interaction of AlCl3+NaF was additive on N. linckia and C. vulgaris, respectively, at pH 7.5 and 6.8, and synergistic at pH 6.0 and 4.5. In the presence of 60 and 100 microM PO4(3-) an increased NaF concentration (in the AlCl3+NaF combination) was required to produce the same degree of inhibition in ATP synthesis and ATPase activity. Toxicity of fluoroaluminate was reduced in the presence of EDTA and citrate. Except for beryllium to some extent, combinations of cadmium, cobalt, iron, manganese, tin and zinc with fluoride were not as effective as aluminium in inhibiting the ATPase activity. The presence of a 100 kDa protein band in SDS-PAGE of both control as well as AlCl3+NaF-treated samples suggested that AlF4- inhibits the ATPase activity by acting as a functional barrier without affecting the structure of the enzyme.
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PMID:Impact of aluminium, fluoride and fluoroaluminate complex on ATPase activity of Nostoc linckia and Chlorella vulgaris. 869 79

The role of endogenous acid was evaluated in a rat model of gastric epithelial damage induced by local ischemia-reperfusion (IR). Because no gross lesion was induced in this model, the damage was quantified by measuring the blood-to-lumen [51Cr]EDTA clearance. A proton pump inhibitor (omeprazole) or an H2-receptor antagonist (T-593) was used to suppress luminal acidity from pH 5 to pH 6.3-7.0. Both drugs significantly attenuated the increase in clearance induced by IR, indicating an important role for endogenous acid. A second series of experiments was performed to confirm whether the change in pH from around 5 to 7 was sufficient to reduce IR-induced gastric mucosal damage. Phosphate-buffered saline was perfused into the gastric lumen to neutralize the endogenous luminal acid. Although the luminal acid was completely neutralized, no reduction in clearance was observed. These data indicate that endogenous luminal acid does not play an important role in gastric injury induced by local IR stress and that a proton pump inhibitor or H2-receptor antagonist may suppress IR injury by a mechanism other than reducing luminal acidity, i.e., reducing consumption of ATP needed for acid secretion, thereby improving gastric mucosal energy metabolism.
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PMID:Role of endogenous acid in gastric mucosal injury induced by local ischemia-reperfusion in the rat. 877 1

We attached human transferrin to Pseudomonas exotoxin A (PE) to specifically localize this toxin to the endosomal compartment and study its translocation from purified endosomes using a cell-free assay. Transferrin was linked to PE via a disulfide bond. Chemical derivatization inactivated the PE cell-binding domain, and transferrin-PE was found to be endocytosed via the transferrin receptor only. Transferrin was also conjugated to a truncated PE with no receptor-binding domain (PE46). After labeling mouse lymphocytes with radiolabeled transferrin-PE or transferrin-PE46 and endosome isolation, selective translocation of the full-sized toxin portion of the conjugate was observed in a cell-free system. This translocation was strictly dependent upon ATP hydrolysis and was not affected when the acidity of the endosome lumen was neutralized using weak bases, protonophores, or bafilomycin A1. Nevertheless, when present during cell labeling, inhibitors of endosome acidification prevented PE from acquiring translocation competence. Similar inhibition was observed when endocytosis was performed in the presence of brefeldin A, a drug known to interfere with the delivery of endocytic tracers to acidic endosomes. Our data indicate that full-length PE can be transferred to the cytosol directly from endosomes during intoxication by PE conjugates and that, although exposure to acidic pH is a prerequisite for translocation, ATP hydrolysis directly provides the energy required for PE translocation.
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PMID:Translocation of full-length Pseudomonas exotoxin from endosomes is driven by ATP hydrolysis but requires prior exposure to acidic pH. 882 63

Acidosis has traditionally been considered to mediate certain types of hypoxic-ischemic injury to the brain. However, the recent demonstration that moderate acidosis will reduce NMDA-mediated currents suggested that acidity could actually protect against types of ischemia and excitotoxicity, and in vitro studies now support this idea. Prompted by this, we have utilized the silicon microphysiometer, a recently-developed instrument that allows for indirect real-time measurement of metabolic rate by detecting proton efflux from small numbers of cultured cells, to determine whether acidity has protective effects upon cellular metabolism. Reducing extracellular pH from 7.4 to as low as 6.0 caused prompt, step-wise, and reversible inhibition of proton efflux rate in cortical and hippocampal cultures both normally and restricted to either glycolysis or oxidative metabolism. Approximately half of the inhibition was due to acidotic effects of NMDA-mediated currents, as demonstrated with NMDA receptor antagonists. Such an inhibition of this indirect metabolic measure could be associated with constant or increased ATP concentrations and represent a beneficial decrease in energy demands upon a neuron. Alternatively, an inhibition of proton efflux rate could be associated with ATP depletion and reflect impaired energy production. We observed a complex interplay between these opposing patterns. Reducing pH to 6.7 for 20 min caused significantly increased ATP concentrations, and prevented excitotoxin-induced ATP depletion. These effects of acidosis involved both NMDA-dependent and- independent actions. More severe (less than pH 6.7) acidosis did not cause ATP concentrations to rise, and if sustained for more than an hour caused a significant decline in ATP concentrations. Thus, despite the recent emphasis on the surprising neuroprotective potential of acidosis, a drop in pH is still likely to have complex and mixed consequences for brain tissue.
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PMID:Salutary and deleterious effects of acidity on an indirect measure of metabolic rate and ATP concentrations in CNS cultures. 888 62

Effects of 3,3',5'-triiodothyronine (rT3) in connection with 3,3',5-triiodothyronine (T3) on 3T3 cells were studied in vitro by means of 1H and 31P NMR spectroscopy. In the cells incubated with 5 nM T3 for 3 h at pH 7.4, the ATP/ADP ratio was elevated from 6.9 to 8.4, whereas it was reduced to 6.1 in cells incubated with rT3. When the cells were incubated at pH 6.7, the ATP/ADP ratio was reduced to 6.6 and 5.2 at 1 and 2 h, respectively. In the presence of 5 nM of T3, however, the ratio was maintained above the control level. A 1-h preincubation with rT3 dramatically augmented the reductions caused by elevated acidity. These reductions were completely reversed when the cells were incubated with T3.
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PMID:Adverse effects of reverse triiodothyronine on cellular metabolism as assessed by 1H and 31P NMR spectroscopy. 944 Jan 39

ATP-driven acidification of internal compartments of Trypanosoma cruzi epimastigotes was assayed spectrophotometrically with Acridine Orange and cells permeabilized with filipin. H+-ATPase activity was not inhibited fully by either 500 nM concanamycin A or 500 microM orthovanadate, but a combination of 5 nM concanamycin A and 25 microM vanadate completely inhibited activity, suggesting the operation of separate V-type (concanamycin-sensitive) and P-type (vanadate-sensitive) H+-ATPase activities in the permeabilized cells. This was supported by different kinetics of Acridine Orange uptake seen in the presence of the different inhibitors, and by different optimal protein (cell) concentrations for the two apparent activities. The use of different buffers further distinguished the ATPases. The V-H+-ATPase activity was stimulated by K+ and inhibited by a lack of anions or the replacement of Cl- with gluconate. The P-type H+-ATPase activity was not affected by a lack of Cl- or K+ but was substantially inhibited in a largely anion-free buffer. This inhibition could be annulled by the addition of the K+ ionophore valinomycin, which probably acted via the establishment of a countercurrent efflux of K+ from the compartment containing the P-type H+-ATPase and the relief of the potential difference generated by the electrogenic proton pump. Valinomycin showed some stimulation of P-type activity in all buffers tested, but its effects on V-H+-ATPase activity were at best transient except in a K+-free buffer, which suggested that the V-H+-ATPase was located in an organelle with relatively low [K+] that was different from that which accommodated the P-type activity. On the basis of acidity and K+ content, these organelles might correspond, in part at least, to the acidocalcisomes (V-H+-ATPase activity) and the reservosomes (P-type activity) previously identified in these cells. Both activities could also be found in the human-infective forms of the parasite, amastigotes and trypomastigotes, but the P-type activity was relatively weak in these cells types, which is correlated with a lack of reservosomes in these forms.
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PMID:Two types of H+-ATPase are involved in the acidification of internal compartments in Trypanosoma cruzi. 953 1

Substrate depletion and increased intracellular acidity are believed to underlie clinically important manifestations of myocardial ischaemia. Recent advances in measuring ion concentrations and metabolite changes have provided a wealth of detail on the processes involved. Coupled with the rapid increase in computing power, this has allowed the development of a mathematical model of cardiac metabolism in normal and ischaemic conditions. Pre-existing models of cardiac cells such as Oxsoft HEART contain highly developed dynamic descriptions of cardiac electrical activity. While biophysically detailed, these models do not yet incorporate biochemical changes. Modelling of bioenergetic changes was based and verified against whole heart NMR spectroscopy. In the model, ATP hydrolysis and generation are calculated simultaneously as a function of [Pi]i. Simulation of pH regulation was based on the pHi dependency of acid efflux, examined in time-course studies of pHi recovery (measured in myocytes with the fluorophore carboxy-SNARF-1) from imposed acid and alkali loads. The force-[Ca2+]i relationship of myofibrils was used as the basis of modelling H+ competition with Ca2+, and thus of pH effects on contraction. This complex description of biochemically important changes in myocardial ischaemia was integrated into the OXSOFT models. The model is sufficiently complete to simulate calcium-overload arrhythmias during ischaemia and reperfusion-induced arrhythmias. The timecourse of both metabolite and pH changes correlates well with clinical and experimental studies. The model possesses predictive power, as it aided the identification of electrophysiological effects of therapeutic interventions such as Na(+)-H+ block. It also suggests a strategy for the control of cardiac arrhythmias during calcium overload by regulating sodium-calcium exchange. In summary, we have developed a biochemically and biophysically detailed model that provides a novel approach to studying myocardial ischaemia and reperfusion.
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PMID:Modelling myocardial ischaemia and reperfusion. 978 54


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