The aging of a brain soluble fraction modifies its effect on the activity of neuronal Na+, K+-ATPase

In previous work we presented evidence showing that a brain soluble fraction was necessary to observe the stimulation of membrane Na+,K+-ATPase activity by catecholamines. Preliminary experiments suggested to us that the soluble fraction by itself was able to modify this enzyme activity. In the present study we have assayed the activity of synaptosomal Na+,K+-ATPase in the presence of a soluble fraction (aqueous supernatant after 100,000 g 30 min) prepared from rat cerebral cortex. The soluble fraction was used at different times after its preparation and different conditions in the incubation period previous to the enzyme assay were tested. It was observed that the enzyme activity increased 70% in the presence of a "0 min" soluble fraction. This effect was not found: a) in the presence of a "30 min" soluble fraction or b) when the membranes plus a "0 min" soluble fraction were incubated for 30 min (15 min at 37 degrees C + 15 min at 0 degree C) before the ATPase assay. In the presence of a "60 min" or "24 h" soluble fraction Na+,K+-ATPase activity was inhibited 50%. Results obtained indicate that Na+,K+-ATPase activity of synaptosomal membranes can be stimulated, inhibited or unchanged, depending on the aging of the soluble fraction.