title: Differential effects of glucose and glyburide on energetics and Na+ levels of betaHC9 cells: nuclear magnetic resonance spectroscopy and respirometry studies.
abstract: In the present study, noninvasive (31)P and (23)Na(+)-nuclear magnetic resonance (NMR) technology and respirometry were used to compare the effect of high glucose (30 mmol/l) with the effect of the antidiabetic sulfonylurea (SU) compound glyburide (GLY) on energy metabolism, Na(+) flux, insulin, and cAMP release of continuously superfused beta-HC9 cells encapsulated in microscopic agarose beads. Both high glucose and GLY increased oxygen consumption in beta-HC9 cells (15-30%) with a maximal effect at 8 mmol/l for glucose and at 250 nmol/l for GLY. At the same time, insulin release from beta-cells increased by 15- and 25-fold with high glucose or GLY, respectively. The P-creatine (PCr) level was greatly increased and inorganic phosphate (P(i)) was decreased with 30 mmol/l glucose in contrast to the decreased level of PCr and increased P(i) with GLY. ATP levels remained unchanged during both interventions. Studies on isolated mitochondria of beta-HC9 cells showed that GLY added to mitochondria oxidizing glutamine or glutamate abolished the stimulation of respiration by ADP (state 3) meanwhile leaving state 3 respiration unchanged during oxidation of other substrates. Exposure of beta-HC9 cells to 5 mmol/l glucose decreased intracellular Na(+) levels monitored by (23)Na(+)-NMR spectroscopy and 30 mmol/l glucose resulted in a further decrease in cytosolic Na(+). In contrast, Na(+) increased when 1 micro mol/l GLY was added to the perfusate containing 5 mmol/l glucose. These data support the hypothesis that glucose activates the beta-cell through a "push mechanism" due to substrate pressure enhancing fuel flux, energy production, and extrusion of Na(+) from the cells in contrast to SU receptor (SUR)-1 inhibitors, which may modify intermediary and energy metabolism secondarily through a "pull mechanism" due to higher energy demand resulting from increased ion fluxes and the exocytotic work load.
authors.affiliation: Diabetes Research Center and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia 19104, USA. nicolai@mail.med.upenn.edu
authors.forename: Nicolai M
authors.initials: NM
authors.lastname: Doliba
authors.forename: Marko Z
authors.initials: MZ
authors.lastname: Vatamaniuk
authors.forename: Carol W
authors.initials: CW
authors.lastname: Buettger
authors.forename: Wei
authors.initials: W
authors.lastname: Qin
authors.forename: Heather W
authors.initials: HW
authors.lastname: Collins
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Wehrli
authors.forename: Richard D
authors.initials: RD
authors.lastname: Carr
authors.forename: Franz M
authors.initials: FM
authors.lastname: Matschinsky
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004734:Energy Metabolism / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D005905:Glyburide / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects*; D010477:Perfusion / Q000379:methods; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D019802:Succinic Acid / Q000378:metabolism
chemical_list: D010725:Phosphocreatine; D005973:Glutamine; D018698:Glutamic Acid; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D019802:Succinic Acid; D005947:Glucose; D005905:Glyburide