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Related Experiment Videos

Ca2+ sparks triggered by patch depolarization in rat heart cells

S R Shorofsky1, L Izu, W G Wier

  • 1Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA.

Circulation Research
|March 20, 1998
PubMed
Summary

Calcium (Ca2+) entry through L-type channels triggers local Ca2+ sparks in heart cells. This study confirms Ca2+ influx, not just voltage, is essential for initiating these sparks, crucial for heart contraction.

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Area of Science:

  • Cardiology
  • Cell Physiology
  • Molecular Biology

Background:

  • Local intracellular calcium ([Ca2+]i) transients, known as Ca2+ sparks, are critical for excitation-contraction coupling in cardiac cells.
  • L-type Ca2+ channels play a pivotal role in regulating Ca2+ influx into cardiac myocytes.

Purpose of the Study:

  • To investigate the relationship between Ca2+ influx via L-type Ca2+ channels and the initiation of local Ca2+ sparks in rat cardiac ventricular cells.
  • To determine whether Ca2+ entry or membrane depolarization itself is the primary trigger for Ca2+ sparks.

Main Methods:

  • Utilized cell-attached patch clamp electrophysiology to activate L-type Ca2+ channels in isolated rat cardiac ventricular cells.
  • Employed laser scanning confocal microscopy to simultaneously measure intracellular Ca2+ ([Ca2+]i) transients (Ca2+ sparks) and L-type Ca2+ channel activity.

Related Experiment Videos

  • Experimentally manipulated charge carriers (Ca2+ or Ba2+) in the pipette solution to differentiate the roles of Ca2+ influx and voltage.

    • Main Results:

    • Depolarization of membrane patches with Ca2+ significantly increased the Ca2+ spark rate in the sub-membrane cytoplasm, while Ba2+ did not.
    • Ca2+ entry, not voltage alone, was identified as a necessary event for triggering Ca2+ sparks.
    • Single L-type Ca2+ channel recordings showed a conductance of 19 pS with Ba2+ and an inward current of up to 0.75 pA with Ca2+.

    Conclusions:

    • Voltage-activated Ca2+ entry through a small number of L-type Ca2+ channels initiates Ca2+ release from the adjacent sarcoplasmic reticulum.
    • Ca2+ influx is the direct trigger for localized Ca2+ sparks in cardiac cells.
    • The study highlights the precise spatial coupling between L-type Ca2+ channels and Ca2+ release units in the heart.