1. 1. The slow alterations in the activity of extracellular Na+ concentrations were measured by using ion-selective electrodes. 2. 2. In the first min there is an increase in the changes of the activity of extracellular Na+ following acetylcholine evoked contractures. 3. 3. This increment was significantly inhibited by k-Strophantoside application, suggesting an active transport origin of this first peak. 4. 4. In the second min a strong decrease in the activity of extracellular Na+ concentration followed. 5. 5. Reducing agent (ascorbate) increased, while oxidant (methylene-blue) decreased both the first increment and the sequential decrement in the activity of the extracellular Na+ concentrations. 6. 6. On the basis of these experiments a site of action of the redox regulation of excitatory processes could be the modification of Na+ fluxes.
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