Glucose metabolism and glutamate analog acutely alkalinize pH of insulin secretory vesicles of pancreatic beta-cells.
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.
Eto
Kazuhiro
K
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
Yamashita
Tokuyuki
T
Hirose
Kenzo
K
Tsubamoto
Yoshiharu
Y
Ainscow
Edward K
EK
Rutter
Guy A
GA
Kimura
Satoshi
S
Noda
Mitsuhiko
M
Iino
Masamitsu
M
Kadowaki
Takashi
T
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
D005456:Fluorescent Dyes; D005971:Glutamates; D007328:Insulin; D015221:Potassium Channels; C035873:glutamic acid dimethyl ester; D000255:Adenosine Triphosphate; D005947:Glucose