title: Glucose-stimulated single pancreatic islets sustain increased cytosolic ATP levels during initial Ca2+ influx and subsequent Ca2+ oscillations.
abstract: In pancreatic islets, insulin secretion occurs via synchronous elevation of Ca(2+) levels throughout the islets during high glucose conditions. This Ca(2+) elevation has two phases: a quick increase, observed after the glucose stimulus, followed by prolonged oscillations. In these processes, the elevation of intracellular ATP levels generated from glucose is assumed to inhibit ATP-sensitive K(+) channels, leading to the depolarization of membranes, which in turn induces Ca(2+) elevation in the islets. However, little is known about the dynamics of intracellular ATP levels and their correlation with Ca(2+) levels in the islets in response to changing glucose levels. In this study, a genetically encoded fluorescent biosensor for ATP and a fluorescent Ca(2+) dye were employed to simultaneously monitor the dynamics of intracellular ATP and Ca(2+) levels, respectively, inside single isolated islets. We observed rapid increases in cytosolic and mitochondrial ATP levels after stimulation with glucose, as well as with methyl pyruvate or leucine/glutamine. High ATP levels were sustained as long as high glucose levels persisted. Inhibition of ATP production suppressed the initial Ca(2+) increase, suggesting that enhanced energy metabolism triggers the initial phase of Ca(2+) influx. On the other hand, cytosolic ATP levels did not fluctuate significantly with the Ca(2+) level in the subsequent oscillation phases. Importantly, Ca(2+) oscillations stopped immediately before ATP levels decreased significantly. These results might explain how food or glucose intake evokes insulin secretion and how the resulting decrease in plasma glucose levels leads to cessation of secretion.
authors.affiliation: From the Graduate School of Biostudies.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nagashima
authors.forename: Nobuya
authors.initials: N
authors.lastname: Inagaki
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Kioka
authors.forename: Seiji
authors.initials: S
authors.lastname: Takashima
authors.forename: Hajime
authors.initials: H
authors.lastname: Fukuoka
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Noji
authors.forename: Akira
authors.initials: A
authors.lastname: Kakizuka
authors.forename: Hiromi
authors.initials: H
authors.lastname: Imamura
mesh_terms: D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D005973:Glutamine / Q000235:genetics / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D007930:Leucine / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D013549:Sweetening Agents / Q000378:metabolism / Q000494:pharmacology
chemical_list: D013549:Sweetening Agents; D005973:Glutamine; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; D007930:Leucine; D005947:Glucose; D002118:Calcium
keywords: ATP; Calcium; Energy Metabolism; Imaging; Insulin; Pancreatic Islets