title: Glucose metabolism and glutamate analog acutely alkalinize pH of insulin secretory vesicles of pancreatic beta-cells.
abstract: We studied acute changes of secretory vesicle pH in pancreatic beta-cells with a fluorescent pH indicator, lysosensor green DND-189. Fluorescence was decreased by 0.66 +/- 0.10% at 149 +/- 16 s with 22.2 mM glucose stimulation, indicating that vesicular pH was alkalinized by approximately 0.016 unit. Glucose-responsive pH increase was observed when cytosolic Ca2+ influx was blocked but disappeared when an inhibitor of glycolysis or mitochondrial ATP synthase was present. Glutamate dimethyl ester (GME), a plasma membrane-permeable analog of glutamate, potentiated glucose-stimulated insulin secretion at 5 mM without changing cellular ATP content or cytosolic Ca2+ concentration ([Ca2+]). Application of GME at basal glucose concentration decreased DND-189 fluorescence by 0.83 +/- 0.19% at 38 +/- 2 s. These results indicated that the acutely alkalinizing effect of glucose on beta-cell secretory vesicle pH was dependent on glucose metabolism but independent of modulations of cytosolic [Ca2+]. Moreover, glutamate derived from glucose may be one of the mediators of this alkalinizing effect of glucose, which may have potential relevance to the alteration of secretory function by glutamate.
authors.affiliation: Dept. of Metabolic Diseases, Graduate School of Medicine, Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. kadowaki-3im@h.u-tokyo.ac.jp
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Eto
authors.forename: Tokuyuki
authors.initials: T
authors.lastname: Yamashita
authors.forename: Kenzo
authors.initials: K
authors.lastname: Hirose
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Tsubamoto
authors.forename: Edward K
authors.initials: EK
authors.lastname: Ainscow
authors.forename: Guy A
authors.initials: GA
authors.lastname: Rutter
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kimura
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Noda
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Iino
authors.forename: Takashi
authors.initials: T
authors.lastname: Kadowaki
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005456:Fluorescent Dyes; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology*; D005971:Glutamates / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D051379:Mice; D008810:Mice, Inbred C57BL; D010084:Oxidation-Reduction; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D022142:Secretory Vesicles / Q000187:drug effects* / Q000378:metabolism
chemical_list: D005456:Fluorescent Dyes; D005971:Glutamates; D007328:Insulin; D015221:Potassium Channels; C035873:glutamic acid dimethyl ester; D000255:Adenosine Triphosphate; D005947:Glucose