Oxygen requirements, morphology, cell coat and membrane permeability of calcium-tolerant myocytes from hearts of adult rats.

The morphological, functional, and biochemical properties of freshly isolated heart muscle cells were examined. A reproducible method for the separation and purification of such cells isolated from adult rat heart was developed. It yields an average of 5 X 10(6) striated rectangular cells which retain normal morphology (range 2.5 to 11 X 10(6) and 4 X 10(6) calcium-tolerant cells (range 2.5 to 5.5 X 10(6) per heart. After purification, 85 to 95% of the cells retain normal morphology in solutions of calcium ion activity equal to 10 microM, and 65 to 79% of the cells are rectangular in solutions of calcium ion activity equal to 1 mM. Under the light microscope we were able to identify functionally intact individual cells that are calcium-tolerant and contract only in response to electrical stimulations, as well as dying myocytes that beat spontaneously. The examination of such cells under the electron microscope permitted us to address the question: What is the sequence of structural changes in a dying cell? The sarcomere lengths measured both in the living state and after preparation for electron microscopy are in the physiological range. In steady states of oxygen tension, respiration of the intact cells is undiminished from 50 torr to 2 torr. The oxygen tension for half maximal respiration is 0.15 torr. Therefore, the limitation of oxygen diffusion to the mitochondria of isolated heart muscle cells must be remarkably small.