The Changes in Adenine Nucleotides Measured in Glucose-stimulated Rodent Islets Occur in β Cells but Not in α Cells and Are Also Observed in Human Islets

Philippe Detimary,Sandra Dejonghe,Zhidong Ling,Daniel Pipeleers,Frans Schuit,Jean-Claude Henquin

doi:10.1074/jbc.273.51.33905

Philippe Detimary, Sandra Dejonghe + Show 4 more

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https://doi.org/10.1074/jbc.273.51.33905

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Abstract

Glucose metabolism by pancreatic beta and alpha cells is essential for stimulation of insulin secretion and inhibition of glucagon secretion. Studies using rodent islets have suggested that the ATP/ADP ratio serves as second messenger in beta cells. This study compared the effects of glucose on glucose oxidation ([U-14C]glucose) and adenine nucleotides (luminometric method) in purified rat alpha and beta cells. The rate of glucose oxidation at 1 mM glucose was higher in beta than alpha cells (4.5-fold, i.e. approximately 2-fold after normalization for cell size). It was more strongly stimulated by 10 mM glucose in beta cells (9-fold) than in alpha cells (5-fold). At 1 mM glucose, ATP levels were similar in both cell types, which corresponds to an approximately 2-fold higher concentration in alpha cells ( approximately 6.5 mM) than in beta cells ( approximately 3 mM). In beta cells, glucose dose-dependently increased ATP and decreased ADP levels, causing a rise in the ATP/ADP ratio from 2.4 to 11.6 at 1 and 10 mM, respectively. In alpha cells, glucose did not affect ATP and ADP levels, and the ATP/ADP ratio remained stable around 7.5. In human islets, the ATP/ADP ratio progressively increased between 1 and 10 mM glucose. In duct cells, which often contaminate human islet preparations, an increase in the ATP/ADP ratio sometimes occurred between 1 and 3 mM glucose. In conclusion, the present observations establish that the regulation of glucagon secretion by glucose does not involve changes in alpha cell adenine nucleotides and further support the role of the ATP/ADP ratio in the control of insulin secretion.

Highlights

Ʈ To whom correspondence should be addressed: United’Endocrinologie et Metabolisme, UCL 55.30, Avenue Hippocrate 55, B 1200 Brussels, Belgium
ATP and ADP levels were slightly lower in purified ␤ cells, but their relative changes were slightly larger, resulting in an increase in the ATP/ADP ratio from 3.2 to 14.8 between 1 and 10 mM glucose
As compared with ␤ cells, the ATP/ADP ratio in islet non-␤ cells was higher at 1 mM glucose but increased much less at 10 mM

Summary

Introduction

Ʈ To whom correspondence should be addressed: United’Endocrinologie et Metabolisme, UCL 55.30, Avenue Hippocrate 55, B 1200 Brussels, Belgium. We demonstrated that glucose causes a large, concentration-dependent increase in the ATP/ADP ratio in mouse islets and that this effect might be involved in the regulation of insulin secretion through both pathways [19, 20]. The changes measured in whole islets might not exactly reflect those occurring in ␤ cells It is not known whether glucose affects adenine nucleotides in ␣ cells. The present study compares the effect of glucose on adenine nucleotides in purified rat ␣ and ␤ cells [23]. It examines whether the changes observed in rodent cells are seen in isolated human islets

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