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Phosphate Accumulation (phosphate + accumulation)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Interplay of constitutively released nucleotides, nucleotide metabolism, and activity of P2Y receptors

DRUG DEVELOPMENT RESEARCH, Issue 2-3 2001
Eduardo R. Lazarowski
Abstract At least six mammalian P2Y receptors exist that are specifically activated by ATP, UTP, ADP or UDP. Although the existence of ectoenzymes that rapidly metabolize extracellular nucleotides is well established, the relative flux of ATP and UTP through their extracellular metabolic products remains undefined. In addition, the existence of basal nucleotide release and the contribution of resting levels of ATP and UTP to P2 receptor activation are poorly understood. In the absence of exogenous agonists, an apyrase-sensitive inositol phosphate accumulation was observed in resting 16HBE14o, human bronchial epithelial cells endogenously expressing P2Y receptors and in 1321N1 human astrocytoma cells expressing a recombinant P2Y2 receptor. To test whether nucleotide release may account for basal P2 receptor activities, the rates of extracellular accumulation and metabolism of endogenous ATP were examined with resting 16HBE14o,, C6 rat glioma, and 1321N1 cell cultures. Although extracellular ATP concentrations (1-5 nM) remained unchanged for up to 12 h, [,32P] ATP included in the medium (as a radiotracer) was completely degraded within 120 min, indicating that ATP release balanced ATP hydrolysis. The calculated basal rates of ATP release ranged from 20 to 200 fmol/min per million cells. HPLC analysis during steady state revealed that the gamma-phosphate of ATP was reversibly transferred to species further identified as UTP and GTP, implicating ecto-nucleoside diphosphokinase (NDPK)-catalyzed phosphorylation of endogenous UDP and GDP. At steady state, the final 32P-products of [,32P]ATP metabolism were 32P-orthophosphoric acid and a species further purified and identified as 32P-pyrophosphate. Constitutive nucleotide release balanced by the concerted activities of ecto-ATPase, ecto-ATP pyrophosphatase, and ecto-NDPK may determine the resting levels of extracellular nucleotides and therefore, the basal activity of P2 receptors. Drug Dev. Res. 53:66,71, 2001. © 2001 Wiley-Liss, Inc. [source]

Involvement of a novel transcriptional activator and small RNA in post-transcriptional regulation of the glucose phosphoenolpyruvate phosphotransferase system

MOLECULAR MICROBIOLOGY, Issue 4 2004
Carin K. Vanderpool
Summary RyaA is a small non-coding RNA in Escherichia coli that was identified by its ability to bind tightly to the RNA chaperone Hfq. This study reports the role of RyaA in mediating the cellular response to glucose-specific phosphoenolypyruvate phosphotransferase system (PTS)-dependent phosphosugar stress. Aiba and co-workers have shown that a block in the metabolism of glucose 6-phosphate causes transient growth inhibition and post-transcriptional regulation of ptsG, encoding the glucose-specific PTS transporter. We found that RyaA synthesis was induced by a non-metabolizable glucose phosphate analogue and was necessary for relief of the toxicity of glucose phosphate stress. Expression of RyaA was sufficient to cause a rapid loss of ptsG mRNA, probably reflecting degradation of the message mediated by RyaA:ptsG pairing. The ryaA gene was renamed sgrS, for sugar transport-related sRNA. Expression of sgrS is regulated by a novel transcriptional activator, SgrR (formerly YabN), which has a putative DNA-binding domain and a solute-binding domain similar to those found in certain transport proteins. Our results suggest that under conditions of glucose phosphate accumulation, SgrR activates SgrS synthesis, causing degradation of ptsG mRNA. Decreased ptsG mRNA results in decreased production of glucose transport machinery, thus limiting further accumulation of glucose phosphate. [source]

Pharmacological characterization of F-180: a selective human V1a vasopressin receptor agonist of high affinity

BRITISH JOURNAL OF PHARMACOLOGY, Issue 7 2002
Miriam Andrés
The pharmacological properties of F-180, a vasopressin (VP) structural analogue, were determined on CHO cells expressing the different human vasopressin and oxytocin (OT) receptor subtypes. Binding experiments revealed that F-180 exhibited a high affinity for the human V1a receptor subtype (Ki=11 nM) and was selective for this receptor subtype. Functional studies performed on CHO cells expressing human V1a receptors indicate that similarly to AVP, F-180 can stimulate the accumulation of inositol phosphate. The activation constant (Kact) for both F-180 and AVP was 1.7 nM. F-180 was also an agonist for the human V2 and V1b receptor subtypes and an antagonist for the human OT receptor. Since marked species pharmacological differences for vasopressin receptors have been described, we studied the properties of F-180 on various mammalian species. F-180 showed high affinity and good selectivity for human and bovine V1a receptors, but weak affinity and non selective properties for rat V1a receptors. To assess the functional properties of F-180 on a native biological model, we performed studies on primary cultures of cells from bovine zona fasciculata (ZF). As AVP, F-180 stimulated inositol phosphate accumulation and cortisol secretion with similar efficiency. In conclusion, we demonstrate that F-180 is the first selective V1a agonist described for human and bovine vasopressin receptors. Therefore F-180 can be used as a powerful pharmacological tool to characterize the actions of vasopressin that are mediated by V1a receptor subtypes. British Journal of Pharmacology (2002) 135, 1828,1836; doi:10.1038/sj.bjp.0704634 [source]

Effects of extracellular nucleotides and nucleosides on prostate carcinoma cells

BRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2001
Rodolphe Janssens
The purpose of this work was to characterize the receptors involved in the action of nucleotides on the human prostate carcinoma cell lines LNCaP, PC-3 and DU145. Northern blotting revealed the presence of P2Y2, P2Y6 and P2Y11 messengers in the three cell lines. P2Y1 mRNA was only observed in the DU145 cells. In both PC-3 and DU145 cells, ATP and UTP stimulated inositol phosphate accumulation in an equipotent, equiactive and non-additive way, suggesting the involvement of P2Y2 receptors. ATP also increased cyclic AMP, but this effect is likely to result from degradation into adenosine and activation of A2 receptor. A2 receptor activation led to a synergistic enhancement of prostate-specific antigen secretion induced by vasoactive intestinal peptide. RT , PCR experiments detected the expression of the P2X4 and P2X5 receptors in the DU145 cells and the P2X4, P2X5 and P2X7 receptors in the PC-3 cells. The calcium influx induced by BzATP confirmed the functional expression of P2X receptors. ATP inhibited the growth of PC-3 and DU145 cells. This effect was mimicked neither by UTP nor by adenosine, indicating that it does not result from phospholipase C or adenylyl cyclase activation. On the contrary, in PC-3 cells, BzATP reproduced the effect of ATP, which was associated to a moderate decrease of proliferation and an increase of apoptosis. In DU145 cells, ATP was more potent than BzATP and growth inhibition was mainly associated with necrosis. We suggest that P2X receptors might be involved in the inhibition by nucleotides of prostate carcinoma cell growth. British Journal of Pharmacology (2001) 132, 536,546; doi:10.1038/sj.bjp.0703833 [source]