Author's present address P. Lipp: The Babraham Institute Laboratory of Molecular Signalling, Babraham Hall, Babraham, Cambridge CB2 4AT, UK.
Fundamental calcium release events revealed by two-photon excitation photolysis of caged calcium in guinea-pig cardiac myocytes
Article first published online: 22 SEP 2004
The Journal of Physiology
Volume 508, Issue 3, pages 801–809, May 1998
How to Cite
Lipp, P. and Niggli, E. (1998), Fundamental calcium release events revealed by two-photon excitation photolysis of caged calcium in guinea-pig cardiac myocytes. The Journal of Physiology, 508: 801–809. doi: 10.1111/j.1469-7793.1998.801bp.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- (Received 11 December 1997; accepted after revision 28 February 1998)
- 1In cardiac muscle, ‘Ca2+ sparks’ have been proposed to underlie Ca2+-induced Ca2+ release (CICR), and to result from openings of clusters of Ca2+ channels (ryanodine receptors; RyRs) located in the sarcoplasmic reticulum membrane.
- 2To investigate the elementary nature of these Ca2+ signals directly, a diffraction-limited point source of Ca2+ was created in single cardiac myocytes by two-photon excitation photolysis of caged Ca2+. Simultaneously, concentration profiles of released Ca2+ were imaged at high temporal and spatial resolution with a laser-scanning confocal microscope.
- 3This approach enabled us to generate and detect photolytic Ca2+ signals that closely resembled the Ca2+ sparks occurring naturally, not only in amplitude and size, but also in their ability to trigger additional Ca2+ sparks or Ca2+ waves.
- 4Surprisingly, at low photolytic power minuscule events with estimated Ca2+ release fluxes 20-40 times smaller than those calculated for a typical Ca2+ spark were directly resolved. These events appeared to arise from the opening of a more limited number of RyRs (possibly one) or from RyRs exhibiting a different gating mode and may correspond to the elusive ‘Ca2+ quark’.
- 5The Ca2+ quark represents the fundamental Ca2+ release event of excitable cells implementing hierarchical Ca2+ signalling systems with Ca2+ release events of various but distinct amplitude levels (i.e. Ca2+ quarks, Ca2+ sparks and full cellular Ca2+ transients).
- 6A graded recruitment of nanoscopic Ca2+ release domains (i.e. Ca2+ quarks) exhibiting variable degrees of spatial coherence and coupling may then build up intermediate Ca2+ signalling events (i.e. Ca2+ sparks). This mechanism suggests the existence of Ca2+ sparks caused by gating of a variable fraction of RyRs from within an individual cluster. Additional mobilization of a variable number of these Ca2+ sparks enables cardiac cells to show graded cellular Ca2+ transients. Similar recruitment processes may underlie regulation of Ca2+ signalling on the cellular level in general.