Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

ATP is co-stored in neurosecretory vesicles together with aminergic compounds and is released from neural cells and synaptic terminals via regulated exocytosis. ATP also is released from non-neuronal cells including astrocytes and astrocyte-like cell lines. However, the mechanism(s) involved in ATP release from astrocytes and other non-secretory cells remains unclear. ATP release from primary astrocytes, astrocytoma, and glioma cells is accompanied by enhanced accumulation of extracellular UTP, and we have recently discovered that in addition to adenine and uridine nucleotides, astrocytoma cells release UDP-glucose. It has been illustrated that agonists that promote Ca2+ mobilization, e.g. thrombin, promote robust release of ATP from 1321N1 astrocytoma cells. Agonist-promoted release of ATP from 1321N1 astrocytoma cells also results in the release of UDP-glucose but, unlike fast hydrolysable ATP, UDP-glucose was hydrolysed at a markedly slow rate. Since UDP-sugars and ATP are concentrated up to 20 times in the lumen of the secretory pathway to serve as substrates for glycosyl transferase and phosphorylation reactions, respectively, we propose that both constitutive and regulated release of nucleotides and nucleotide-sugars from astrocytes involves a vesicular mechanism. Observation that adenine nucleotides, uridine nucleotides, and UDP-sugars are released from both resting and stimulated astrocytes provides support for the physiological significance of nucleotide- and UDP-sugar-sensing P2Y receptors in the brain. These findings also suggest that slow hydrolysable UDP-glucose may accomplish long lasting signalling on P2Y14 receptors expressed in astrocytes.
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PMID:Regulated release of nucleotides and UDP sugars from astrocytoma cells. 1680 24

The human P2Y(14) receptor is potently activated by UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), UDP-N-acetylglucosamine (UDP-GlcNAc), and UDP-glucuronic acid. Recently, cellular release of UDP-Glc and UDP-GlcNAc has been reported, but whether additional UDP-sugars are endogenous agonists for the P2Y(14) receptor remains poorly defined. In the present study, we describe an assay for the quantification of UDP-Gal with subnanomolar sensitivity. This assay is based on the enzymatic conversion of UDP-Gal to UDP, using 1-4-beta-galactosyltransferase. UDP is subsequently phosphorylated by nucleoside diphosphokinase in the presence of [gamma-(32)P]ATP and the formation of [gamma-(32)P]UTP is monitored by high-performance liquid chromatography. The overall conversion of UDP-Gal to [gamma-(32)P]UTP was linear between 0.5 and 30 nM UDP-Gal. Extracellular UDP-Gal was detected on resting cultures of various cell types, and increased release of UDP-Gal was observed in 1321N1 human astrocytoma cells stimulated with the protease-activated receptor agonist thrombin. The occurrence of regulated release of UDP-Gal suggests that, in addition to its role in glycosylation reactions, UDP-Gal is an important extracellular signaling molecule.
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PMID:Quantification of extracellular UDP-galactose. 1969 3