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Related Experiment Videos

Action currents generate stepwise intracellular Ca2+ patterns in a neuroendocrine cell

J R Lieste1, W J Koopman, V C Reynen

  • 1Department of Cellular Animal Physiology, Institute of Cellular Signaling and Nijmegen Institute for Neurosciences, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.

The Journal of Biological Chemistry
|September 25, 1998
PubMed
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Calcium (Ca2+) steps control cellular functions. This study reveals Ca2+ channels, not Na+ channels, generate these steps, with their pattern determined by action currents and Ca2+ removal rates.

Area of Science:

  • Cellular biology
  • Neuroendocrinology
  • Calcium signaling

Background:

  • Cytosolic-free calcium concentration ([Ca2+]i) patterns regulate crucial cellular processes.
  • Calcium (Ca2+) oscillations in Xenopus laevis melanotrope cells consist of discrete Ca2+ steps.
  • The origin and role of these Ca2+ steps in generating Ca2+ patterns were previously unknown.

Purpose of the Study:

  • To investigate the origin of Ca2+ steps in melanotrope cells.
  • To determine the role of action currents and ion channels in generating Ca2+ oscillations.
  • To elucidate the factors controlling the specific patterns of Ca2+ oscillations.

Main Methods:

  • Simultaneous, noninvasive measurement of melanotrope plasma membrane electrical activity and [Ca2+]i.

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  • Utilized tetrodotoxin (Na+ channel blocker) and CoCl2 (Ca2+ channel blocker).
  • Performed experiments under Na+-free conditions and with high K+ stimulation.

    • Main Results:

    • Ca2+ step characteristics (number, amplitude, frequency) vary and depend on action current firing patterns.
    • Tetrodotoxin did not affect action currents or [Ca2+]i.
    • CoCl2 abolished action currents and Ca2+ steps, indicating Ca2+ channels are essential.
    • Ca2+ removal rate is dependent on [Ca2+]i, even during oscillation rising phases.

    Conclusions:

    • Calcium (Ca2+) channels, not sodium (Na+) channels, are critical for generating specific Ca2+ step patterns.
    • The interplay between Ca2+ action current frequency/shape and cytoplasmic Ca2+ removal rate dictates the oscillatory pattern.
    • This provides a mechanistic understanding of how specific Ca2+ oscillation patterns are formed.