Selective astrocytic gap junctional trafficking of molecules involved in the glycolytic pathway: impact on cellular brain imaging

• Published in: Journal of neurochemistry Vol. 110; no. 3; pp. 857 - 869
• Main Authors: Gandhi, Gautam K, Cruz, Nancy F, Ball, Kelly K, Theus, Sue A, Dienel, Gerald A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.08.2009; Blackwell Publishing Ltd; Wiley-Blackwell
• Subjects: Animals; astrocyte; Astrocytes - cytology; Astrocytes - metabolism; Autoradiography; Biochemistry; Biochemistry and metabolism; Biological and medical sciences; Brain - cytology; Brain - metabolism; brain imaging; Cells, Cultured; Cellular biology; Central nervous system; Cerebral circulation. Blood-brain barrier. Choroid plexus. Cerebrospinal fluid. Circumventricular organ. Meninges; connexin; Fundamental and applied biological sciences. Psychology; gap junction; Gap Junctions - metabolism; Glycolysis - physiology; hexose-6-phosphate; Magnetic Resonance Spectroscopy; Male; Medical imaging; Metabolism; Microscopy, Fluorescence; NAD(P)H fluorescence; Neurology; Protein Transport - physiology; Rats; Rats, Wistar; Vertebrates: nervous system and sense organs; NADPH; Phosphates; brain imaging; Metabolite; NAD(P)H fluorescence; Neuroglia; Central nervous system; Cell junction; Fluorescence; Astrocyte; Glucose; Gap junction; Encephalon; Specificity; NADH; hexose-6-phosphate; Intracellular; Diffusion; connexin
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2009.06173.x

To assess the specificity of metabolite trafficking among gap junction-coupled astrocytes, we developed novel, real-time, single-cell enzymatic fluorescence assays to assay cell-to-cell transfer of unlabeled glycolytic intermediates and report (i) highly restricted transfer of glucose-6-phosphate (P) and two analogs, deoxyglucose (DG)-6-P, and 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-DG-6-P, compared with DG and 2- and 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-DG, (ii) extensive junctional diffusion of glyceraldehyde-3-P, NADH, and NADPH plus three anionic fluorescent dyes used as internal standards for transfer assays, and (iii) stimulation of gap junctional communication by increased intracellular Na⁺ that also evokes metabolic responses in nearby coupled astrocytes. Thus, dye transfer does not predict gap junctional permeability of endogenous metabolites. Intracellular retention of flux-regulating compounds (e.g. glucose-6-P) may be necessary for local metabolic control, whereas 'syncytial sharing' may dissipate the work load on peri-synaptic astrocytes. Imaging of brain functional activity depends on local accumulation of exogenous or endogenous signals, and DG-6-P is trapped in the cell where it is phosphorylated, whereas rapid dispersal of cytoplasmic NAD(P)H and labeled glucose metabolites throughout the astrocytic syncytium can interfere with cellular assessment of neuron-astrocyte relationships in autoradiographic, fluorescence microscopic, and magnetic resonance spectroscopic studies.