The endoplasmic reticulum is a glucose-modulated high-affinity sink for Ca2+ in mouse pancreatic beta-cells

J Physiol. 2001 Feb 1;530(Pt 3):533-40. doi: 10.1111/j.1469-7793.2001.0533k.x.

Abstract

The regulation of organelle free Ca2+ was analysed in individual mouse pancreatic beta-cells loaded with the fluorescent low-affinity indicator furaptra. Removal of the cytoplasmic indicator by controlled digitonin permeabilization of the plasma membrane resulted in a sudden increase of the 340 nm/380 nm fluorescence excitation ratio followed by a gradual decay, reflecting the emptying of Ca2+ from organelle pools. Subsequent introduction of 3 mM ATP caused rapid refilling of a Ca2+ pool, which represented the endoplasmic reticulum (ER) in being mobilized with inositol 1,4,5-trisphosphate (IP3) and the sarco(endo)plasmic reticulum Ca2+-ATPase inhibitor thapsigargin. The concentration of Ca2+ in the ER observed immediately after permeabilization depended on the glucose concentration in a hyperbolic fashion with half-maximal filling at about 6 mM of the sugar. Glucose promotion of Ca2+ sequestration in the ER involved a high-affinity mechanism not requiring but accelerated by a rise of the cytoplasmic Ca2+ concentration. Glucose also exerted a long-term action on the ER storage of Ca2+, maintaining the set-point for its maximal concentration and preserving the response to IP3. The results indicate that the ER has an important role in the glucose-stimulated beta-cell by serving as a high-affinity sink for Ca2+, irrespective of the prevailing concentration of cytoplasmic Ca2+.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Animals
  • Biological Transport
  • Calcium / metabolism*
  • Cells, Cultured
  • Endoplasmic Reticulum / drug effects
  • Endoplasmic Reticulum / physiology*
  • Fluorescent Dyes
  • Fura-2 / analogs & derivatives*
  • Glucose / pharmacology*
  • Inositol 1,4,5-Trisphosphate / pharmacology
  • Islets of Langerhans / physiology*
  • Kinetics
  • Mice
  • Mice, Obese
  • Organelles / drug effects
  • Organelles / physiology
  • Thapsigargin / pharmacology

Substances

  • Fluorescent Dyes
  • 2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid
  • Thapsigargin
  • Inositol 1,4,5-Trisphosphate
  • Adenosine Triphosphate
  • Glucose
  • Calcium
  • Fura-2