Temperature-sensitive random insulin granule diffusion is a prerequisite for recruiting granules for release

Traffic. 2004 Oct;5(10):750-62. doi: 10.1111/j.1600-0854.2004.00216.x.

Abstract

Glucose-evoked insulin secretion exhibits a biphasic time course and is associated with accelerated intracellular granule movement. We combined live confocal imaging of EGFP-labelled insulin granules with capacitance measurements of exocytosis in clonal INS-1 cells to explore the relation between distinct random and directed modes of insulin granule movement, as well as exocytotic capacity. Reducing the temperature from 34 degrees C to 24 degrees C caused a dramatic 81% drop in the frequency of directed events, but reduced directed velocities by a mere 25%. The much stronger temperature sensitivity of the frequency of directed events (estimated energy of activation approximately 135 kJ/mol) than that of the granule velocities (approximately 22 kJ/mol) suggests that cooling-induced suppression of insulin granule movement is attributable to factors other than reduced motor protein adenosine 5'-triphosphatase activity. Indeed, cooling suppresses random granule diffusion by approximately 50%. In the single cell, the number of directed events depends on the extent of granule diffusion. Finally, single-cell exocytosis exhibits a biphasic pattern corresponding to that observed in vivo, and only the component reflecting 2nd phase insulin secretion is affected by cooling. We conclude that random diffusive movement is a prerequisite for directed insulin granule transport and for the recruitment of insulin granules released during 2nd phase insulin secretion.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Diffusion
  • Electrophysiology
  • Exocytosis / physiology*
  • Green Fluorescent Proteins
  • Immunohistochemistry
  • Insulin / metabolism*
  • Insulin Secretion
  • Microscopy, Confocal
  • Protein Transport / physiology
  • Rats
  • Secretory Vesicles / metabolism*
  • Temperature*
  • Transfection
  • Tumor Cells, Cultured

Substances

  • Insulin
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins