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Query: UMLS:C0220723 (PCA)
 4,687 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Immediately after stimulation with glucose in vitro, isolated rat pancreatic islets prelabeled with [32P]orthophosphate release a pulse of [32P]orthophosphate into the media (the "phosphate flush"). Islets have been rapidly frozen before, during, and after this pulse to assess the concurrent changes in the distribution of tissue radioactivity. Under the present experimental conditions, approximately 90% of the islet radioactivity was soluble in perchloric acid (PCA-soluble) immediately before stimulation and slightly more than half of that was present as [32P]orthophosphate. The tissue pool of [32P]orthophosphate declined 55% and 62% after 7 and 14 min of stimulation which, respectively, incorporated the peak and the end of the heightened efflux of radioactivity. The net decrementa in tissue orthophosphate could account for all of the radioactivity which was released during the "phosphate flush." During the 14-min period of stimulation, labeled ATP and GTP (which had accounted for 13% and 4% of total PCA-soluble radioactivity before stimulation) increased 51% and 35%, respectively, and labeled ADP and AMP (which had accounted for 5.4% and 1.5% of PCA-soluble counts) fell 36% and 77%, respectively. Certain other PCA-soluble components, such as phosphorylcholine and phosphorylethanolamine, and total PCA-insoluble radioactivity were not demonstrably altered. The findings indicate that the "phosphate flush" originates from a labile pool of tissue orthophosphate. It remains to be established whether the simultaneous changes in the turnover of selected nucleotides are coupled to the translocation of orthophosphate or are mediated separately.
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PMID:32P-labeling patterns in rat pancreatic islets: tissue source of the radiophosphate released after glucose stimulation. 36 45

Under conditions where cytochalasin B induces ATPase activity of monomeric actin (0.3 mM MgCl2, 1 mM EGTA, 30 microns cytochalasin B, 1 mM ATP) the rate constant of the exchange of actin-bound epsilon-ATP for free ATP is about 4-6 times faster than steady state ATPase activity. When a stoichiometric ATP-actin complex is extracted with PCA (single turnover experiment) the apparent rate constant of Pi generation is not faster than steady state ATPase activity. - The experiments suggest that the hydrolysis of actin-bound ATP and not the subsequent release of hydrolysis products is rate-limiting during cytochalasin-induced ATPase activity of actin.
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PMID:Product release is not the rate-limiting step during cytochalasin B-induced ATPase activity of monomeric actin. 182 56

A method for a simultaneous separation of malondialdehyde (MDA), ascorbic acid and adenine nucleotide derivatives in biological samples by ion-pairing high-performance liquid chromatography is presented. The separation is obtained by an LC-18-T 15 cm x 4.6 mm 3 microns particle size column using tetrabutylammonium as the pairing ion. The starting buffer consists of 10 mM tetrabutylammonium hydroxide, 10 mM KH2PO4 plus 1% methanol, pH 7.00. A step gradient is formed using a second buffer consisting of 2.8 mM tetrabutylammonium hydroxide, 100 mM KH2PO4 plus 30% methanol, pH 5.5. Under these chromatographic conditions a highly resolved separation of MDA, ATP, ADP, AMP, adenosine, ascorbic acid, GTP, GDP, IMP, inosine, Hypoxanthine, Xanthine, uric acid, NAD, and NADP can be performed in about 36 min. In addition, the separation of NADH and NADPH can also be obtained; this renders the present method suitable for the detection of these reduced coenzymes in alkaline extracts from tissue samples. Data referring to PCA extracts from ischemic and reperfused isolated rat hearts and from human erythrocytes peroxidized in vitro by a challenge with 1 mM NaN3 and various concentrations of H2O2 are reported. The relevance of this chromatographic method lies in the possibility to determine directly MDA concentrations avoiding the unspecific thiobarbituric acid colorimetric test, any other manipulation of the sample out of the PCA extraction, and any possible coelution of other acid soluble compounds. The simultaneous determination of MDA, ascorbic acid, and of ATP and its degradation products gives the opportunity to correlate, by a single chromatographic run, peroxidative damages with the energy state of the cell which is of great importance in studies of ischemic and reperfused tissues.
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PMID:Simultaneous separation of malondialdehyde, ascorbic acid, and adenine nucleotide derivatives from biological samples by ion-pairing high-performance liquid chromatography. 195 65

PCA 4233 [2-(phenylthio)ethyl-5-ethoxycarbonyl-2,4,6-trimethyl- 1,4-dihydropyridine-3-carboxylate] and PCA 4248 [2-(phenylthio) ethyl-5-methoxycarbonyl-2, 4, 6-trimethyl-1, 4-dihydropyridine-3-carboxylate], two compounds developed from a series of 1,4-dihydropyridines that lack pharmacologic effects on voltage-operated calcium channels, were found to block selectively rabbit operated calcium channels, were found to block selectively rabbit and human platelet aggregation and secretion, and binding of [3H]-labeled platelet-activating factor (PAF) to human platelet and polymorphonuclear PAF receptors. Rabbit platelet aggregation was tested with 1.9 nM PAF, i.e., a concentration producing maximal response, and was completely blocked with 10 microM PCA 4233 and 3 microM 4248 (IC50 values, 2.55 and 1.05 microM, respectively). Human platelet aggregation in platelet-rich plasma was studied with 1 microM PAF, a concentration that caused a response comparable with that of 1.9 nM PAF in rabbit platelets. The IC50 of PCA 4248 for ATP release under these conditions was 3.6 microM. PCA 4248 behaved as a competitive and selective antagonist in [3H]serotonin secretion studies on rabbit platelets, since it displaced rightwards log dose-response curves and lacked any effect on thrombin- and ionophore A23187-induced platelet secretion. A pA2 value of 7.5 was obtained from Schild plots on [3H]serotonin secretion studies. PCA 4248 also produced a dose-dependent inhibition of [3H]PAF binding to human platelets and to human polymorphonuclear leukocytes. These data indicate that PCA 4233 and PCA 4248 belong to a new class of selective PAF-receptor antagonists.
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PMID:1,4-Dihydropyridines, a new class of platelet-activating factor receptor antagonists: in vitro pharmacologic studies. 217 Jun 24

The Malachite Green method for determination of inorganic phosphate (Pi) (Itaya K. & Ui, M. (1966) Clin. Chim. Acta 14, 361-366) was modified to measure Pi in the range of 0.2-15 nmol per ml of ATPase reaction mixture. An ATPase reaction mixture is quenched with an equal volume of 0.6 M PCA; the supernatant after centrifugation is mixed with an equal volume of the Malachite Green/molybdate reagent containing 2 g of sodium molybdate, 0.3 g of Malachite Green and 0.5 g of Triton X-100 or Sterox SE in 1 liter of 0.7 M HCl, and the absorbance at 650 nm is then measured after a 35-40 min incubation at 25 degrees C. Owing to the high sensitivity and simplicity of the modified method, the slow time course of myosin ATP hydrolysis in the presence of Mg2+ and the size of initial phosphate burst can be determined accurately using relatively low concentrations of native myosin and its subfragment-1. The phosphate burst size varied with changes in pH, ionic strength, and temperature. A typical value was 0.8-0.9 mol per site in 0.1 M KCl, 10 mM MgCl2, pH 8.0 at 25 degrees C for fresh enzyme preparations.
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PMID:The initial phosphate burst in ATP hydrolysis by myosin and subfragment-1 as studied by a modified malachite green method for determination of inorganic phosphate. 294 Feb 37

Thiophosphorylation and phosphorylation of 5% perchloric acid extractable proteins from calf thymus chromatin were studied using a cyclic GMP-dependent protein kinase from bovine lung and a nuclear protein kinase II from rat liver. The phosphorylation reaction catalyzed by nuclear protein kinase II utilized [gamma -35S]ATP as a phosphate donor almost as efficiently as [gamma -32P]ATP, but the cGMP-dependent protein kinase mediated phosphorylation by [35S]ATP was about 20 times less effective than that by [32P]ATP. In addition, using [35S]ATP instead of [32P]ATP changed markedly the cGMP-dependent phosphorylation pattern of the PCA-extractable proteins as examined by gel electrophoresis. Thus, depending on the type of protein kinase, the results from thiophosphorylation and phosphorylation reactions may vary considerably.
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PMID:Thiophosphorylation and phosphorylation of chromatin proteins from calf thymus in vitro. 298 63

A bioassay, using high-performance liquid chromatography (HPLC) analysis of platelet adenosine nucleotides and hypoxanthine, was studied for its potential use as a test for MH susceptibility. A protocol for the assay was developed, based on the method outlined by Solomons and Masson. The HPLC procedure was a rapid, efficient, sensitive, and highly reproducible technique for measuring ATP, ADP, AMP, and hypoxanthine in platelets. Conditions of extraction and storage were critical for preventing degradation of the nucleotides. Extraction of nucleotides at icebath temperature was found necessary. Storage of platelet extract in PCA, even at -20 degrees C, showed loss of ATP and ADP; hence, neutralization with KOH was essential before storage. Contrary to the findings of Solomons et al., the present study demonstrated that neither ATP depletion nor per cent reduction in nucleotide ratios in platelets treated with halothane can be used as a definitive test for the diagnosis of MH susceptibility. The reason for this disagreement is unclear; however, differences in methods and altitude are implicated. It is possible that the platelet is not affected by malignant hyperthermia and thus cannot serve as a test system for the detection of the syndrome.
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PMID:The use of a platelet nucleotide assay as a possible diagnostic test for malignant hyperthermia. 402 92

The spectrum of low molecular weight compounds, in particular of ribonucleotides, within first cleavage stage embryos of the polar lobe-forming mollusc Nassarius reticulatus and the distribution of the compounds within the embryo at the trefoil stage of first cleavage are analysed by means of capillary isotachophoresis after 0.5 M PCA extraction. The compounds which are found in the whole trefoil embryo (T), the lobeless part (LL), and the polar lobe (PL) respectively, and the mean quantities (nmol. microliter-1; n = 6) are: UTP (11.5, 4.8, 5.6), ITP (8.5, 3.6, 5.0), GTP (10.3, 3.0, 9.0), ATP (29.8, 13.4, 18.8), UDP (11.8, 3.4, 8.7), CTP (8.0, 3.1, 4.5), GDP (5.3, 2.6, 3.4), ADP (16.5, 6.1, 11.6), CDP (4.0, 1.4, 2.6), GMP (4.7, 2.7, 4.3), glucose-6-phosphate (G6P) (53.5, 38.8, 13.0). These compounds appear to be localized in the non-yolk cytoplasmic pool. As the volume ratio of PL/LL for total volume and for non-yolk cytoplasmic volume is about 0.74 and 0.60 respectively, the concentration of all nucleotides in PL as compared to LL is significantly higher (HO, p less than 0.001), both relative to the total volume and to the non-yolk cytoplasmic volume. The G6P concentration is considerably higher in the lobeless part. The morphogenetic role of the vegetal pole compartment of the egg apparently is correlated with a relatively high level of its nucleotide contents.
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PMID:Composition of the nucleotides pool in a morphogenetic compartment in eggs of Nassarius reticulatus (Mollusca) analysed by capillary isotachophoresis. 406 27

ATP, ADP, AMP and glycerate 2, 3-bisphosphate in blood are frequently analyzed in order to evaluate erythrocytes for blood donation and to diagnose hemolytic anemias. In order to find an uncomplicated and safe procedure for the preanalytical treatment of blood a freezing-storing procedure using dry ice was worked out and combined with a later PCA precipitation. The pre-freezing stability of the components was also investigated and found to be best at room temperature.
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PMID:Specimen handling for the assay of adenylates and glycerate 2, 3-bisphosphate in erythrocytes. 731 20

The PACAPs have been shown to be potent vasodilators in different animal species. Data in humans are still lacking. Therefore we investigated the effects of PACAP 38, PACAP 27 and VIP on isolated human and porcine coronary arteries (HCA and PCA). Our data show, that the PACAPs are endothelium-independent vasorelaxants, which in HCA are slightly more potent than VIP. The N-terminal shortened peptides PACAP 6-38 and PACAP 6-27 also show relatively potent vasorelaxant effects, acting as partial agonists. Glibenclamide, a selective inhibitor of ATP-sensitive potassium channels, partially reverses the effects of the PACAPs, indicating an involvement of these channels in the mechanism of action.
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PMID:Pituitary adenylate cyclase activating peptides are endothelium-independent dilators of human and porcine coronary arteries. 771 91


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