Cheng HP*, Lederer WJ, Cannell MB, Calcium sparks: The elementary events underlying excitation-contraction coupling in heart muscle. SCIENCE, 262, 740-744,1993.

Abstract Spontaneous local increases in the concentration of intracellular calcium, called "calcium sparks," were detected in quiescent rat heart cells with a laser scanning confocal microscope and the fluorescent calcium indicator fluo-3. Estimates of calcium flux associated with the sparks suggest that calcium sparks result from spontaneous openings of single sarcoplasmic reticulum (SR) calcium-release channels, a finding supported by ryanodine-dependent changes of spark kinetics. At resting intracellular calcium concentrations, these SR calcium-release channels had a low rate of opening (approximately 0.0001 per second). An increase in the calcium content of the SR, however, was associated with a fourfold increase in opening rate and resulted in some sparks triggering propagating waves......