Stimulation and inhibition of synaptosome ATPases by noradrenaline. The involvement of cytoplasmic factor.

The activity of Na+, K+-ATPase was determined in synaptosomes and in pellets, (containing membranes, mitochondria and vesicles) and cytoplasm prepared from synaptosomes from rat cerebral cortex. The activity of the pellets was more than two fold higher than that of the synaptosomes or of their components and adding back the cytoplasm reduced the activity of the pellets. Noradrenaline did not affect the activity of the pellets but increased that of the synaptosomes in a dose-dependent fashion. It inhibited the activity of the membranes. Results indicate that synaptosomal Na+, K+-ATPase activity is low because of a factor in the cytoplasm and this factor is not present in synaptosome pellets. NA antagonises the activity of the factor.