The role of cardiac mitochondria in the regulation of intracellular calcium during ischemia and reperfusion: X-ray microanalysis using freeze-dried sections.

The calcium concentration in papillary muscles was measured by X-ray microanalysis in order to clarify the role played by mitochondria in intracellular calcium regulation during ischemia and reperfusion. Rat hearts perfused by the Langendorff method were rapidly frozen prior to and during ischemia, as well as following reperfusion. Sections prepared by cryoultramicrotomy were freeze-dried, carbon-coated, and analyzed in an electron microscope. A new freeze-drying procedure was developed, in which the ultrastructure was well-preserved, with sarcomeres, triads, and mitochondria easily recognized. Calcium accumulation into the mitochondria occurred during 30-min ischemia (29.7 +/- 17.0 mmol/kg dry weight) and increased further after 15-min reperfusion (157.1 +/- 104.5), the calcium concentration decreased after 60-min reperfusion (58.1 +/- 29.0). However, the calcium concentration in the cytosol did not change significantly. It is thought that mitochondrial calcium accumulation is reversible, to a certain degree, and that the mitochondria play a part in intracellular calcium regulation in pathological states.