title: Temporal patterns of changes in ATP/ADP ratio, glucose 6-phosphate and cytoplasmic free Ca2+ in glucose-stimulated pancreatic beta-cells.
abstract: Closure of ATP-sensitive K+ (K(ATP)) channels is part of the stimulus-secretion coupling mechanism in the pancreatic beta-cell, leading to membrane depolarization and influx of Ca2+ through voltage-sensitive L-type Ca2+ channels. The elevated ATP/ADP ratio seen in the presence of high levels of glucose has been postulated to mediate the glucose-induced closure of the K(ATP) channels and rise in cytoplasmic free Ca2+ concentration ([Ca2+]i), or alternatively to be a consequence of activation of mitochondrial dehydrogenases by the increase in [Ca2+]i. To distinguish between these two possibilities, the time course of the change in the ATP/ADP ratio was determined in comparison with that of [Ca2+]i. We here show that a severalfold rise in the ATP/ADP ratio occurs rapidly on stimulation of suspensions of mouse pancreatic beta-cells with glucose. The change in the ATP/ADP ratio is an early event that begins within 20-40 s and precedes the rise in [Ca2+]i. The temporal relationship indicates that the adenine nucleotide changes cannot be a consequence of the [Ca2+]i changes and may indeed be the connecting link between glucose metabolism and [Ca2+]i changes. When the cells were sequentially treated with high glucose concentration, clonidine and finally high extracellular Ca2+ concentration to induce synchronized oscillations in [Ca2+]i in the cell suspension, corresponding oscillations in the ATP/ADP ratio were observed. Glucose 6-phosphate levels oscillated out of phase with the ATP/ADP ratio. These results support the hypothesis that the Ca2+ oscillations previously observed in glucose-stimulated single islets or beta-cells may reflect oscillations in the ATP/ADP ratio that accompany oscillatory glycolysis.
authors.affiliation: Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Nilsson
authors.forename: V
authors.initials: V
authors.lastname: Schultz
authors.forename: P O
authors.initials: PO
authors.lastname: Berggren
authors.forename: B E
authors.initials: BE
authors.lastname: Corkey
authors.forename: K
authors.initials: K
authors.lastname: Tornheim
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003000:Clonidine / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism*; D006019:Glycolysis; D007515:Islets of Langerhans / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008820:Mice, Obese; D015221:Potassium Channels / Q000378:metabolism
chemical_list: D000316:Adrenergic alpha-Agonists; D005958:Glucosephosphates; D015221:Potassium Channels; D019298:Glucose-6-Phosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005947:Glucose; D003000:Clonidine; D002118:Calcium