Predominant role of active versus facilitative glucose transport for glucagon-like peptide-1 secretion

Diabetologia. 2012 Sep;55(9):2445-55. doi: 10.1007/s00125-012-2585-2. Epub 2012 May 26.

Abstract

Aims/hypothesis: Several glucose-sensing pathways have been implicated in glucose-triggered secretion of glucagon-like peptide-1 (GLP-1) from intestinal L cells. One involves glucose metabolism and closure of ATP-sensitive K(+) channels, and another exploits the electrogenic nature of Na(+)-coupled glucose transporters (SGLTs). This study aimed to elucidate the role of these distinct mechanisms in glucose-stimulated GLP-1 secretion.

Methods: Glucose uptake into L cells (either GLUTag cells or cells in primary cultures, using a new transgenic mouse model combining proglucagon promoter-driven Cre recombinase with a ROSA26tdRFP reporter) was monitored with the FLII(12)Pglu-700 μδ6 glucose sensor. Effects of pharmacological and genetic interference with SGLT1 or facilitative glucose transport (GLUT) on intracellular glucose accumulation and metabolism (measured by NAD(P)H autofluorescence), cytosolic Ca(2+) (monitored with Fura2) and GLP-1 secretion (assayed by ELISA) were assessed.

Results: L cell glucose uptake was dominated by GLUT-mediated transport, being abolished by phloretin but not phloridzin. NAD(P)H autofluorescence was glucose dependent and enhanced by a glucokinase activator. In GLUTag cells, but not primary L cells, phloretin partially impaired glucose-dependent secretion, and suppressed an amplifying effect of glucose under depolarising high K(+) conditions. The key importance of SGLT1 in GLUTag and primary cells was evident from the impairment of secretion by phloridzin or Sglt1 knockdown and failure of glucose to trigger cytosolic Ca(2+) elevation in primary L cells from Sglt1 knockout mice.

Conclusions/interpretation: SGLT1 acts as the luminal glucose sensor in L cells, but intracellular glucose concentrations are largely determined by GLUT activity. Although L cell glucose metabolism depends partially on glucokinase activity, this plays only a minor role in glucose-stimulated GLP-1 secretion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport
  • Cell Line
  • Cells, Cultured
  • Enteroendocrine Cells / metabolism*
  • Flow Cytometry
  • Gene Expression Regulation
  • Glucagon / metabolism
  • Glucagon-Like Peptide 1 / metabolism*
  • Immunohistochemistry
  • Intestines / pathology*
  • KATP Channels / metabolism*
  • Mice
  • Mice, Knockout
  • Phloretin / pharmacology*
  • Sodium-Glucose Transporter 1 / metabolism*

Substances

  • KATP Channels
  • Slc5a1 protein, mouse
  • Sodium-Glucose Transporter 1
  • Glucagon-Like Peptide 1
  • Glucagon
  • Phloretin