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Calcium diffusion coefficient in Myxicola axoplasm

N F al-Baldawi1, R F Abercrombie

  • 1Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, USA.

Cell Calcium
|June 1, 1995
PubMed
Summary

Calcium diffusion in Myxicola axoplasm is slower with intact organelles but increases significantly when organelles are depleted or removed. This suggests mobile calcium-binding sites contribute to buffering capacity.

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Area of Science:

  • Cell Biology
  • Biophysics

Background:

  • Calcium ions (Ca2+) are crucial intracellular messengers.
  • Understanding calcium diffusion dynamics is vital for cellular processes.

Purpose of the Study:

  • To measure calcium diffusion coefficients in Myxicola axoplasm.
  • To investigate the influence of organelles and ATP depletion on calcium diffusion.

Main Methods:

  • Utilized two independent techniques: 45Ca isotope tracing and Ca-specific mini-electrodes.
  • Measured diffusion in intact axoplasm, ATP-depleted axoplasm, and organelle-free axoplasm.

Main Results:

  • Lowest diffusion coefficient (0.1 x 10^-6 cm²/s) observed in intact axoplasm with sequestering organelles.
  • ATP-depleted axoplasm showed diffusion coefficients of 0.5-2 x 10^-6 cm²/s.
  • Organelle-free axoplasm exhibited higher diffusion coefficients (1.4-3 x 10^-6 cm²/s at 0.7 µM Ca, 7 x 10^-6 cm²/s at 3-5 µM Ca).

Conclusions:

  • Calcium diffusion is significantly modulated by intracellular organelles and ATP levels.
  • The measured diffusion coefficients, when compared to buffering capacity, indicate the presence of mobile calcium-binding sites within the axoplasm.

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