A postulated mechanism for the coordinate effects of ionophore A23187 on calcium uptake and cell viability in rat thymocytes.

At the physiological concentration of Ca2+, the presumed calcium ionophore A23187 produced dose-related increases in 45Ca uptake by rat thymocytes and decreases in cell viability, effects that displayed a strong linear correlation. In media containing a very low concentration of Ca2+ (7.10(-6) M), in contrast, ionophore A23187 had no specific effect on either 45Ca uptake or cell viability. The calcium-dependent cytotoxicity of ionophore A23187 resembles that of other agents that are not ionophores, but that are known to perturb the plasma membrane. Consequently, we suggest that, in the rat thymocyte, ionophore, ionophore A23187 may not act as a true ionophore, but may perturb the cell membrane, allowing Ca2+ to pass freely through the membrane along its electrochemical gradient.