Ca2+ and electrolyte mobilization following agonist application to the pancreatic beta cell line HIT

Pflugers Arch. 2000 Oct;440(6):828-34. doi: 10.1007/s004240000372.

Abstract

We have investigated intracellular Ca2+ mobilization in oscillations of cytoplasmic Ca2+ in response to glucagon-like peptide 1 (GLP-1) and glucose in clonal HIT insulinoma cells with a confocal laser-scanning microscope (CLSM). We also used electron probe X-ray microanalysis to determine the GLP-1- and glucose-induced changes in electrolyte levels in the cytoplasm and insulin granules of the cells. GLP-1 produced 10- to 35-s duration oscillations in cytoplasmic Ca2+ concentration ([Ca2+]i), both with and without Ca2+ in the extracellular solution, suggesting that Ca2+ is mobilized from intracellular Ca2+ stores, namely secretory granules. Glucose caused 1- to 3-min duration oscillatory increases in [Ca2+]i when the extracellular solution contained Ca2+. When the cells were cultured without Ca2+ (no Ca2+ added, 1 mM EGTA), an oscillatory [Ca2+]i increase of amplitude and short duration (12-35 s) was produced by 11 mM glucose, and the oscillation was inhibited by ruthenium red. X-ray microanalysis showed that stimulation with glucose increased the total Ca concentration in the cytoplasm and decreased it in the insulin granules with and without Ca2+ in the extracellular solution. The application of glucose significantly decreased K, and increased Na and C1 in the cytoplasm when the extracellular solution contained Ca2+. Our result also suggests that the [Ca2+]i oscillation induced by glucose is involved in the release of Ca2+ from intracellular Ca2+ stores through the ryanodine receptor, which is blocked by ruthenium red, and/or through the inositol trisphosphate receptor that may be present in the membrane of insulin granules.

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Cytoplasm / metabolism
  • Cytoplasmic Granules / metabolism
  • Electrolytes / metabolism*
  • Electron Probe Microanalysis
  • Extracellular Space / metabolism
  • Glucagon / pharmacology*
  • Glucagon-Like Peptide 1
  • Insulinoma
  • Islets of Langerhans / drug effects*
  • Islets of Langerhans / metabolism*
  • Islets of Langerhans / ultrastructure
  • Microscopy, Confocal
  • Microscopy, Electron
  • Pancreatic Neoplasms
  • Peptide Fragments / pharmacology*
  • Protein Precursors / pharmacology*
  • Tumor Cells, Cultured

Substances

  • Electrolytes
  • Peptide Fragments
  • Protein Precursors
  • Glucagon-Like Peptide 1
  • Glucagon
  • Calcium