Cytosolic free calcium in chick heart cells. Its role in cell injury.

The role of cytosolic free Ca2+ (Caf) in cell injury was investigated using two methods for measuring Caf in freshly disaggregated embryonic chick heart cells. The null-point method, using arsenazo III, is based on determining the extracellular Ca2+ concentration at which no net Ca2+ movement occurs when plasma membrane permeability is increased. With this technique, the null point Caf averaged 0.23 +/- 0.07 microM (n = 6) in the basal state. Using quin2, an intracellular fluorescent dye, to measure Caf a value of 0.05 +/- 0.01 microM (n = 5) was obtained. Elevation of Caf by various agents was associated with an increase in cell injury as measured by the release of the cytosolic enzyme, LDH. However, the relationship between Caf and LDH release was not a direct one under all experimental conditions, indicating that the level of Caf is not the sole determinant of cell injury.