DISTRIBUTION OF CALCIUM IN A SUBSET OF CHRONIC HIBERNATING MYOCARDIUMIN MAN

The structural correlates of 'chronic hibernating myocardium' in man c onsist of myocardial cells which transformed from a functional state ( rich in contractile material) to a surviving state (poor in contractil e material, rich in glycogen). Since the calcium-handling organelles s uch as SR, sarcolemma and mitochondria underwent structural changes in cells so affected, the distribution of calcium was investigated in bi opsies obtained from 'hibernating' areas. The material was processed f or microscopic localization of total calcium (laser microprobe mass an alysis, LAMMA) and of exchangeable calcium (phosphate-pyroantimonate p recipitation method, PPA). Subcellular distribution of total calcium a s assessed by LAMMA revealed that in the structurally affected cells t he areas in which sarcomeres were replaced by glycogen contained signi ficantly more calcium than all other areas probed such as mitochondria , remaining sarcomeres at the cell periphery and subcellular areas of normally structured cells. Calcium precipitate, obtained after PPA ass essment, was localized at the sarcolemma but was virtually absent in t he mitochondria of affected cells. The high calcium content in the myo lytic areas of affected cells most probably belongs to a pool of bound calcium. The observations that calcium is retained at the sarcolemma and that mitochondria are devoid of precipitate favour the hypothesis that cells structurally affected as such are not ischaemic and are sti ll able to regulate their calcium homeostasis.