Laser backscatter studies of intracellular Ca2+ oscillations in isolated hearts

We measured intensity fluctuations of 633 nm laser light backscattered from the epicardial surface of isolated, perfused rat and rabbit hearts. Scattered light intensity fluctuations (SLIF) were detected from verapamil-arrested rat hearts. The frequency of SLIF was increased by maneuvers that raise intracellular calcium. SLIF were abolished by removal of extracellular calcium with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and by blockade of sarcoplasmic reticulum calcium release by ryanodine. SLIF were not accompanied by any surface electro-cardiogram and were not abolished by 144 mM extracellular potassium. SLIF were absent in rabbit hearts under base-line conditions but could be provoked by calcium loading using zero potassium and ouabain. We conclude that backscatter SLIF monitor the microscopic motion caused by intracellular calcium oscillations in the intact heart. We measured SLIF from rat hearts during 60 min of global ischemia at 30 degrees C, followed by reflow. Ischemia reduced SLIF frequency to zero within 30 min. Reflow caused an overshoot of SLIF frequency to as much as five times control, suggesting that reflow causes major calcium overload of cells that are at least transiently viable.