title: Chronic hypoxia enhances adenosine release in rat PC12 cells by altering adenosine metabolism and membrane transport.
abstract: Acute exposure to hypoxia causes a release of adenosine (ADO) that is inversely related to the O2 levels in oxygen-sensitive pheochromocytoma (PC12) cells. In the current study, chronic exposure (48 h) of PC12 cells to moderate hypoxia (5% O2) significantly enhanced the release of ADO during severe, acute hypoxia (1% O2). Investigation into the intra- and extracellular mechanisms underpinning the secretion of ADO in PC12 cells chronically exposed to hypoxia revealed changes in gene expression and activities of several key enzymes associated with ADO production and metabolism, as well as the down-regulation of a nucleoside transporter. Decreases in the enzymatic activities of ADO kinase and ADO deaminase accompanied by an increase in those of cytoplasmic and ecto-5'-nucleotidases bring about an increased capacity to produce intra- and extracellular ADO. This increased potential to generate ADO and decreased capacity to metabolize ADO indicate that PC12 cells shift toward an ADO producer phenotype during hypoxia. The reduced function of the rat equilibrative nucleoside transporter rENT1 also plays a role in controlling extracellular ADO levels. The hypoxia-induced alterations in the ADO metabolic enzymes and the rENT1 transporter seem to increase the extracellular concentration of ADO. The biological significance of this regulation is unclear but is likely to be associated with modulating cellular activity during hypoxia.
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati, Ohio 45267-0576, USA.
authors.forename: S
authors.initials: S
authors.lastname: Kobayashi
authors.forename: H
authors.initials: H
authors.lastname: Zimmermann
authors.forename: D E
authors.initials: DE
authors.lastname: Millhorn
mesh_terms: D015720:5'-Nucleotidase / Q000378:metabolism; D000241:Adenosine / Q000378:metabolism*; D000248:Adenosine Kinase / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D043383:Adenosylhomocysteinase; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D015870:Gene Expression / Q000502:physiology; D006867:Hydrolases / Q000235:genetics; D008565:Membrane Proteins / Q000378:metabolism; D016716:PC12 Cells / Q000378:metabolism*; D051381:Rats; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D002352:Carrier Proteins; D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D008565:Membrane Proteins; C438652:Slc29a1 protein, rat; C438655:Slc29a2 protein, rat; D000255:Adenosine Triphosphate; D000248:Adenosine Kinase; D006867:Hydrolases; D015720:5'-Nucleotidase; D043383:Adenosylhomocysteinase; D000241:Adenosine