Cell injury of cultured rat myocardial cells after reoxygenation of hypoxic cultures in the presence and absence of calcium.

Primary cultures of rat myocytes were deprived of oxygen (approximately 5 mm Hg, pO2) for 2 h in the presence or absence of calcium and were subsequently incubated for different time periods under normoxic (approximately 120 mm Hg, pO2) conditions. Myocyte calcium content was determined at the end of the oxygen-free period and after repletion of oxygen. Lactate dehydrogenase (LDH) release from the cells into the medium was used as an index of cell injury. Cultures deprived of oxygen in the absence of calcium showed a significant decrease in myocyte calcium content at the end of the oxygen-free period. However, the calcium content of myocyte cultures deprived of oxygen in the presence of calcium did not change significantly. The enzyme release of both groups of oxygen-deprived cultures was similar to that of controls. A progressive increase in myocyte calcium content was observed 5, 10, 15, and 30 min after repletion of oxygen in both groups. Reoxygenation of cultures subjected to hypoxia in the presence of calcium caused minimal LDH leakage. However, major enzyme release was observed 30 min after oxygen repletion in cultures previously subjected to hypoxia in a calcium-free environment. The present study shows that reoxygenation injury is more severe in myocyte cultures previously deprived of both oxygen and calcium than in cultures deprived of oxygen in the presence of calcium.