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Diabetes. 2010 May;59(5):1192-201. doi: 10.2337/db09-0791. Epub 2010 Feb 11.

Progression of diet-induced diabetes in C57BL6J mice involves functional dissociation of Ca2(+) channels from secretory vesicles.

Author information

1
Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK. stephan.collins@drl.ox.ac.uk

Abstract

OBJECTIVE:

The aim of the study was to elucidate the cellular mechanism underlying the suppression of glucose-induced insulin secretion in mice fed a high-fat diet (HFD) for 15 weeks.

RESEARCH DESIGN AND METHODS:

C57BL6J mice were fed a HFD or a normal diet (ND) for 3 or 15 weeks. Plasma insulin and glucose levels in vivo were assessed by intraperitoneal glucose tolerance test. Insulin secretion in vitro was studied using static incubations and a perfused pancreas preparation. Membrane currents, electrical activity, and exocytosis were examined by patch-clamp technique measurements. Intracellular calcium concentration ([Ca(2+)](i)) was measured by microfluorimetry. Total internal reflection fluorescence microscope (TIRFM) was used for optical imaging of exocytosis and submembrane depolarization-evoked [Ca(2+)](i). The functional data were complemented by analyses of histology and gene transcription.

RESULTS:

After 15 weeks, but not 3 weeks, mice on HFD exhibited hyperglycemia and hypoinsulinemia. Pancreatic islet content and beta-cell area increased 2- and 1.5-fold, respectively. These changes correlated with a 20-50% reduction of glucose-induced insulin secretion (normalized to insulin content). The latter effect was not associated with impaired electrical activity or [Ca(2+)](i) signaling. Single-cell capacitance and TIRFM measurements of exocytosis revealed a selective suppression (>70%) of exocytosis elicited by short (50 ms) depolarization, whereas the responses to longer depolarizations were (500 ms) less affected. The loss of rapid exocytosis correlated with dispersion of Ca(2+) entry in HFD beta-cells. No changes in gene transcription of key exocytotic protein were observed.

CONCLUSIONS:

HFD results in reduced insulin secretion by causing the functional dissociation of voltage-gated Ca(2+) entry from exocytosis. These observations suggest a novel explanation to the well-established link between obesity and diabetes.

PMID:
20150285
PMCID:
PMC2857899
DOI:
10.2337/db09-0791
[Indexed for MEDLINE]
Free PMC Article

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