期刊
DIABETES
卷 51, 期 7, 页码 2056-2065出版社
AMER DIABETES ASSOC
DOI: 10.2337/diabetes.51.7.2056
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资金
- NIDDK NIH HHS [DK 53181] Funding Source: Medline
- NINDS NIH HHS [1F32 NS 10335-01] Funding Source: Medline
Specialized neurons utilize glucose as a signaling molecule to alter their firing rate. Glucose-excited (GE) neurons increase and glucose-inhibited (GI) neurons reduce activity as ambient glucose levels rise. Glucose-induced changes in the ATP-to-ADP ratio in GE neurons modulate the activity of the ATP-sensitive K+ channel, which determines the rate of cell firing. The GI glucosensing mechanism is unknown. We postulated that glucokinase (GK), a high-Michaelis constant (K-m) hexokinase expressed in brain areas containing populations of GE and GI neurons, is the controlling step in glucosensing. Double-label in situ hybridization demonstrated neuron-specific GK mRNA expression in locus ceruleus norepinephrine and in hypothalamic neuropeptide Y, pro-opiomelanocortin, and gamma-aminobutyric acid neurons, but it did not demonstrate this expression in orexin neurons. GK mRNA was also found in the area postrema/nucleus tractus solitarius region by RT-PCR. Intracarotid glucose infusions stimulated c-fos expression in the same areas that expressed GK. At 2.5 mmol/l glucose, fura-2 Ca2+ imaging of dissociated ventromedial hypothalamic nucleus neurons demonstrated GE neurons whose intracellular Ca2+ oscillations were inhibited and GI neurons whose Ca2+ oscillations were stimulated by four selective GK inhibitors. Finally, GK expression was increased in rats with impaired central glucosensing (posthypoglycemia, and diet-induced obesity) but was unaffected by a 48-h fast. These data suggest a critical role for GK as a regulator of glucosensing in both GE and GI neurons in the brain.
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