Effects of anticonvulsant and convulsant drugs on the ATPase activities of synaptosomes and their components.

1. The effects of anticonvulsants, and other drugs on the Na+, K+-adenosine triphosphatase (ATPase) (ouabain-sensitive) and Mg++-ATPase activities of synaptosomes and their components have been determined. 2. The Mg++-ATPase activity of synaptosomes was not affected by the drugs but the Na+, K+-ATPase activity was inhibited by phenytoin (diphenylhydantoin), ethosuximide and diazepam. 3. Fractions containing mainly membranes, mitochondria or synaptic vesicles, were prepared from synaptosomes by osmotic shock and subsequent density gradient centrifugation. Inhibition of Na+, K+-ATPase activity by phenytoin, ethosuximide and diazepam was apparent only in the membrane fraction. 4. The fraction containing synaptic vesicles exhibited pronounced Md++-ATPase but no Na+, K+-ATPase activity. In contrast to the enzymes of the membranes and mitochondria, the Mg++-ATPase of the vesicles was inhibited by diazepam and all of the anticonvulsants tested.