title: Carbon dioxide influence on nitric oxide production in endothelial cells and astrocytes: cellular mechanisms.
abstract: Cerebral vessels may regulate cerebral blood flow by responding to changes in carbon dioxide (CO(2)) through nitric oxide (NO) production. To better determine the role of NO production by human adult cerebral microvascular endothelial cells and human fetal astrocytes under different CO(2) conditions, we studied endothelial cell and astrocyte production of NO under hypo-, normo- and hypercapnic conditions. Human cerebral endothelial cell and fetal astrocyte cultures were exposed to hypocapnic (pCO(2) 21.7±6.7mmHg), normocapnic (pCO(2) 40.1±0.9mmHg) and hypercapnic (pCO(2) 56.3±8.7mmHg) conditions. NO production was recorded continuously over 24hours with stable pH. N-nitro-l-arginine [NLA; a nitric oxide synthase (NOS) inhibitor] and l-arginine (substrate for NO production via NOS) were used to further define the role of NOS in chemoregulation. NO levels in endothelial cells increased during hypercapnia by 36% in 8hours and remained 25% above baseline. NO increase in astrocytes was 30% after 1hour but returned to baseline at 8hours. NLA blocked NO increase in endothelial cells under hypercapnia. During hypocapnia, NO levels in the endothelial cells decreased by 30% at 8hours but were unchanged in astrocytes. l-arginine prevented NO decrease in endothelial cells under hypocapnia. NO changes in the endothelial cells correlated with changes in pCO(2) (R=0.99) and were independent of pH. This study suggests that cerebral endothelial cells and astrocytes release NO under normocapnic conditions and NO production is increased during hypercapnia and decreased during hypocapnia independent of pH. Further, this demonstrates that endothelial cells may play a pivotal role in chemoregulation by modulating NOS activity.
authors.affiliation: Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-1414, USA.
authors.forename: Ali R
authors.initials: AR
authors.lastname: Fathi
authors.forename: Chunzhang
authors.initials: C
authors.lastname: Yang
authors.forename: Kamran D
authors.initials: KD
authors.lastname: Bakhtian
authors.forename: Meng
authors.initials: M
authors.lastname: Qi
authors.forename: Russell R
authors.initials: RR
authors.lastname: Lonser
authors.forename: Ryszard M
authors.initials: RM
authors.lastname: Pluta
mesh_terms: D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D002536:Cerebral Arteries / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D005333:Fetus; D006801:Humans; D009569:Nitric Oxide / Q000096:biosynthesis*; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I