2005 Fiscal Year Final Research Report Summary
Molecular characterization of congenital hyperinsulinism/hyperammonemia caused by glutamate dehydrogenase gene defects
| Project/Area Number |
15390687
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Pediatrics
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| Research Institution | Osaka City University |
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Principal Investigator |
OKANO Yoshiyuki Osaka City University, Department of Pediatrics, Lecturer, 大学院・医学研究科, 講師 (60231213)
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| Co-Investigator(Kenkyū-buntansha) |
INADA Hiroshi Osaka City University, Department of Pediatrics, Lecturer, 大学院・医学研究科, 講師 (00244640)
KAWAMURA Tomoyuki Osaka City University, Department of Pediatrics, Assistant Professor, 大学院・医学研究科, 助手 (60271186)
KUNO Miyuki Osaka City University, Department of physiology, Research Assistant, 大学院・医学研究科, 助教授 (00145773)
MIYAZAKI Jyun-ichi Osaka University, Graduate School of Medicine, Division of Stem Cell Regulation Research, Professor, 大学院・医学系研究科, 教授 (10200156)
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| Project Period (FY) |
2003 – 2005
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| Keywords | glutamate dehydrogenase / insulin / hyperammonemia / hypoglycemia / mutation / K_<ATP> channel / nonselective cation channel |
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| Research Abstract |
The hyperinsulinism/hyperammonemia (HI/HA) syndrome is caused by "gain of function" of glutamate dehydrogenase (GDH). Several missense mutations have been found ; however, cell behaviors triggered by the excessive GDH activity have not been fully demonstrated. This study was aimed to clarify electrophysiological mechanisms underlying the dysregulated insulin secretion in pancreatic beta cells with GDH mutations. GDH kinetics and insulin secretion were measured in MIN6 cells overexpressing the G446D and L413V. Membrane potentials and channel activity were recorded under the perforated-patch configuration that preserved intracellular environments. In mutant MIN6 cells, sensitivity of GDH to guanosine triphosphate (GTP) was reduced and insulin secretion at low glucose concentrations was enhanced. The basal GDH activity was elevated in L413V bearing a mutation in the antenna-like structure. The L413V cells were depolarized without glucose, often accompanying by repetitive Ca^<2+> firings. The depolarization was maintained in the presence of adenosine triphosphate (ATP) and disappeared by depleting ATP, suggesting that the depolarization depended on intracellular ATP. In L413V cells, the ATP-sensitive potassium channel (KATP channel) was suppressed and the nonselective cation channel (NSCC) was potentiated, while sensitivity of the channels to their specific blockers or agonists was not impaired. These data suggest that the L413V cells increase the intracellular ATP/adenosine diphosphate (ADP) ratio, which in turn causes sustained depolarization not only by closure of the KATP channel, but also by opening of the NSCC. The resultant activation of the voltagegated Ca^<2+> channel appears to induce hyperinsulinism. The present study provides evidence that multiple channels cooperate in unregulated insulin secretion in pancreatic beta cells of the HI/HA syndrome.
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