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Related Experiment Videos

Caffeine-stimulated GTH-II release involves Ca(2+) stores with novel properties.

James D Johnson1, Calvin J H Wong, Warren K Yunker

  • 1Department of Biological Sciences, Biological Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.

American Journal of Physiology. Cell Physiology
|February 8, 2002
PubMed
Summary

Caffeine robustly stimulates gonadotropin (GTH-II) release from goldfish cells by affecting calcium stores. This caffeine signaling pathway for GTH-II release differs from typical mechanisms involving endoplasmic reticulum calcium stores.

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Area of Science:

  • Endocrinology
  • Cell Biology
  • Neuroscience

Background:

  • Gonadotropin (GTH-II) release from goldfish gonadotropes is modulated by intracellular calcium (Ca2+) stores.
  • Both endogenous forms of gonadotropin-releasing hormone (GnRH) use a common intracellular Ca2+ store, but sGnRH, not cGnRH-II, utilizes an additional caffeine-sensitive mechanism.

Purpose of the Study:

  • To investigate the specific mechanisms of caffeine signaling in stimulating GTH-II release from goldfish gonadotropes.
  • To differentiate caffeine-induced GTH-II release from pathways activated by GnRH.

Main Methods:

  • Calcium (Ca2+) imaging to visualize intracellular calcium dynamics.
  • Electrophysiology to assess ion channel activity.
  • Cell-column perifusion to measure GTH-II secretion.

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Main Results:

  • Caffeine (10 mM) robustly stimulated GTH-II secretion, independent of K+ channel inhibition and the cAMP/protein kinase A pathway.
  • Caffeine-evoked GTH-II release was Ca2+ signal-dependent, initiated by localized Ca2+ signals near secretory granules.
  • Unlike GnRH, caffeine-stimulated GTH-II release was insensitive to ryanodine, voltage-gated Ca2+ channel inhibitors, and sarco(endo)plasmic reticulum Ca2+-ATPases.

Conclusions:

  • Caffeine stimulates GTH-II release through a Ca2+ signaling pathway distinct from typical agonist-sensitive stores in the endoplasmic reticulum.
  • The mechanism of caffeine-induced GTH-II release in goldfish gonadotropes involves novel Ca2+ mobilization pathways.