however more calcium is required to activate it than usual (i.e. the RyR is in an adaptation phase). This would mean that one-by-one the RyRs would close, thus ending the spark. Sticky cluster theory This theory suggests that the above three theories all play a role in preventing calcium release. Discovery Spontaneous Ca2+ sparks were discovered in cardiac muscle cells, of rats, in 1992 by Peace Cheng and Mark B. Cannell in Jon Lederer's laboratory at the University of Maryland, Baltimore, U.S.A. Initially the idea was rejected by the scientific journal, Nature, who believed that the sparks were only present under laboratory conditions (i.e. they were artifacts), and so wouldn't occur naturally within the body. However they were quickly recognised as being of fundamental importance to muscle physiology, playing a huge role in excitation-contraction coupling. The discovery was made possible due to improvements in confocal microscopes. This allowed for the detection of the release of Ca2+, which were highlighted using a substance known as fluo-3, which caused the Ca2+ to glow. Ca2+ “sparks” were so called because of the spontaneous, localised nature of the Ca2+ release as well as the fact that they are the initiation event of excitation-contraction coupling. Detection and analysis Because of the importance of Ca2+ sparks in explaining the gating properties of ryanodine receptors in situ (within the body), many studies have focused on improving their detectability in the hope that by accurately and reliably detecting all Ca2+ spark events, their true properties can finally help us to answer the unsolved mystery of spark termination. See also Calcium-induced calcium release Confocal microscopy Ryanodine receptor References External links Software SparkMaster - Automated Ca2+ Spark Analysis with ImageJ - Free software for Ca2+ spark analysis in confocal linescan images Cell biology