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Regulatory volume decrease of pancreatic beta-cells involving activation of tetraethylammonium-sensitive K+

A Marcström1, P E Lund, B Hellman

  • 1Department of Medical Cell Biology, University of Uppsala, Sweden.

Molecular and Cellular Biochemistry
|July 17, 1990
PubMed
Summary

Hypotonic stress triggers significant insulin release from pancreatic beta-cells. This response involves water entry, not ion movement, and activates tetraethylammonium-sensitive potassium channels for volume regulation.

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Area of Science:

  • Endocrinology
  • Cell Physiology

Background:

  • Pancreatic beta-cells regulate glucose homeostasis through insulin secretion.
  • Cellular responses to osmotic stress are crucial for maintaining cell volume and function.

Purpose of the Study:

  • To investigate the early effects of hypotonic stress on pancreatic beta-cells.
  • To elucidate the mechanisms underlying insulin release and ion flux during osmotic challenges.

Main Methods:

  • Utilized beta-cell-rich pancreatic islets from ob/ob-mice.
  • Applied hypotonic stress (102 mOsm reduction) and measured insulin release.
  • Assessed ion fluxes (potassium, sodium) and utilized patch-clamp analysis.
  • Tested the effects of various inhibitors (quinine, tetraethylammonium, bumetanide, amiloride, sulfonylureas).

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Main Results:

  • Hypotonic stress induced a transient, 25-fold stimulation of insulin release.
  • Observed a significant loss of potassium without major changes in sodium.
  • Insulin release was independent of quinine and tetraethylammonium.
  • Potassium loss was modulated by quinine and tetraethylammonium, indicating involvement of K+ channels.
  • Patch clamp revealed increased small channel openings, suggesting activation of K+ conductance.

Conclusions:

  • Pancreatic beta-cells exhibit regulatory volume decrease via tetraethylammonium-sensitive K+ channels.
  • Stimulation of insulin release under hypotonic conditions is primarily due to water influx.
  • Ion movements are involved in beta-cell volume readjustment but not directly in osmotic-stimulated insulin secretion.