Calcium ionophore A23187 action on cardiac myocytes is accompanied by enhanced production of reactive oxygen species

We show that rat neonatal cardiac myocytes exposed to 1 μmol/l of the calcium ionophore A23187 respond with an enhanced production of reactive oxygen species (ROS). This dose is not cytotoxic to the myocytes. A higher concentration (10 μmol/l) evokes less ROS production and is significantly cytotoxic 24 h after exposure, but not immediately after removal of the A23187, when ROS are measured. Both cell death and the decrease in mitochondrial potential are only partially sensitive to MPT inhibitor cyclosporin A. Experiments performed to elucidate the sources of ROS included use of the nitric oxide synthase (NOS) inhibitor L-NAME; NOS involvement was excluded. Experiments with the oxidative phosphorylation uncoupler CCCP revealed that mitochondria are at least partially responsible for the observed effect. Further studies with cyclooxygenase (COX) and lipoxygenase (LOX) inhibitors (indomethacin and MK886, respectively) showed that these enzymes could also be sources of ROS when the calcium level is elevated. Their effect appeared to be independent of phospholipase A2 inhibition, suggesting that COX and LOX stimulation is not due to elevated substrate (arachidonic acid) concentration but rather to a direct effect of calcium.