Influence of quinidine on ATP-linked calcium binding by heart mitochondria and microsomes

The action of quinidine on heart microsomal and mitochondrial calcium binding in the presence of MgATP was studied under different experimental conditions and compared with other antiarrhythmic agents such as procaine amide and lidocaine. Quinidine stimulated microsomal calcium binding but depressed mitochondrial calcium binding. Although procaine amide stimulated microsomal calcium binding, it did not affect mitochondrial calcium binding. On the other hand, lidocaine depressed calcium binding by mitochondria without affecting calcium binding by the microsomal fraction. The stimulation of microsomal calcium binding by quinidine was not apparent at high concentrations of Mg2+, low concentrations of ATP, or low concentrations of Ca2+. The depressant action of quinidine on mitochondrial calcium binding was not observed at low concentrations of Mg2+ or ATP but was more pronounced at low concentrations of Ca2+. These results suggest that the action of quinidine on mitochondria may play a major role in eliciting cardiodepressant effect.