Submicroscopic calcium signals as fundamental events of excitation--contraction coupling in guinea-pig cardiac myocytes

J Physiol. 1996 Apr 1;492 ( Pt 1)(Pt 1):31-8. doi: 10.1113/jphysiol.1996.sp021286.


1. Subcellularly localized Ca2+ signals have been proposed to represent elementary events of cardiac Ca2+ signalling (Ca2+ sparks), whereby an individual sarcolemmal L-type Ca2+ channel locally controls opening of a single (or a few) Ca2+ release channels in the sarcoplasmic reticulum (SR). 2. To investigate directly the elementary nature of this Ca(2+)-induced Ca2+ release mechanism we used flash photolysis of caged Ca2+ while simultaneously measuring the intracellular Ca2+ concentration ([Ca2+]i) with a laser-scanning confocal microscope. 3. Power spectral analysis of the confocal images performed in the spatial domain revealed that only Ca2+ signalling events involving the L-type Ca2+ channel pathway gave rise to Ca2+ sparks. In contrast, SR Ca2+ release triggered by photolytic [Ca2+]i jumps resulted in Ca2+ transients that were always spatially homogeneous. 4. From these findings we conclude that the fundamental event of Ca2+ signalling in cardiac muscle may be smaller in size or amplitude than a Ca2+ spark. 5. We term this event a 'Ca2+ quark' possibly resulting from gating of a single SR Ca2+ release channel. It is proposed that concerted activation of several 'Ca2+ quarks' may be required for a Ca2+ spark. The 'Ca2+ quark' could also be the fundamental event in other cell types implementing a hierarchical Ca2+ signalling concept.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calcium Channels / physiology
  • Guinea Pigs
  • Microscopy, Confocal
  • Myocardial Contraction / physiology*
  • Patch-Clamp Techniques
  • Sarcolemma / physiology
  • Sarcoplasmic Reticulum / physiology
  • Ventricular Function*


  • Calcium Channels
  • Calcium