Isolated calcium-tolerant myocytes and the calcium paradox: an ultrastructural comparison.

The ultrastructure of calcium-tolerant myocytes isolated from adult rat ventricular myocardium is described, using thin section and freeze-fracture electron microscopy. Two distinct cell types are observed, rounded and rod-shaped. The former are damaged myocytes and superficially resemble the disrupted cells characteristic of the calcium paradox. Despite this resemblance however, the genesis of these isolated damaged cells is not explicable in terms of the calcium paradox. The majority of isolated cells are rod-shaped and show well preserved ultrastructural features. Our results indicate that whatever mechanisms underlie the calcium paradox it is not an indispensable condition that isolation of myocytes necessarily leads to this phenomenon.