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Related Experiment Videos

Large currents generate cardiac Ca2+ sparks.

L T Izu1, J R Mauban, C W Balke

  • 1Department of Medicine, University of Maryland, Baltimore, Baltimore, Maryland 21201, USA. lizu@umaryland.edu

Biophysical Journal
|February 13, 2001
PubMed
Summary
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Cardiac calcium (Ca2+) sparks are larger than previously modeled, requiring significantly higher Ca2+ currents (10-20 pA) through calcium release units (CRUs) to explain observed spark sizes and durations.

Area of Science:

  • Cardiovascular Physiology
  • Calcium Signaling
  • Biophysics

Background:

  • Previous models of cardiac Ca2+ sparks assumed low Ca2+ currents (1-2 pA) and smaller spark amplitudes (F/F(0) ~2.0, FWHM ~1 µm).
  • These models did not fully account for the observed characteristics of experimentally measured Ca2+ sparks.

Purpose of the Study:

  • To present actual cardiac Ca2+ spark data with larger amplitudes and widths.
  • To develop a mathematical model that explains these larger sparks.
  • To determine the necessary Ca2+ currents through calcium release units (CRUs) to generate observed spark properties.

Main Methods:

  • Analysis of experimentally recorded cardiac Ca2+ sparks.
  • Development of a mathematical model incorporating Ca2+ dynamics and CRU currents.

Related Experiment Videos

  • Simulation of spark generation under varying current densities and buffering conditions.

    • Main Results:

    • Observed Ca2+ sparks exhibited peak fluorescence ratios (F/F(0)) >6 and full-width at half maximum (FWHM) ~2 µm.
    • The mathematical model indicated a lower bound of ~11 pA for CRU current under ideal conditions.
    • Realistic conditions necessitate CRU currents of approximately 20 pA to generate 2-µm Ca2+ sparks.
    • Spark amplitudes (F/F(0)) were significantly larger (6-12) for currents ≥5 pA.
    • Simulations showed that clustered CRUs, each producing ~10 pA, could also generate wider sparks.

    Conclusions:

    • Cardiac Ca2+ sparks possess significantly larger peak amplitudes than previously assumed.
    • The observed spark dimensions (FWHM ~2 µm) are consistent with larger underlying Ca2+ currents (10-20 pA).
    • The findings necessitate a revision of existing models of calcium release unit function in cardiac cells.