Molecular Pharmacology, Vol 5, 593-604, Copyright © 1969 by the American Society for Pharmacology and Experimental Therapeutics

Mechanism of Biogenic Amine Transport

II. Relationship between Sodium and the Mechanism of Ouabain Blockade of the Accumulation of Serotonin and Norepinephrine by Synaptosomes

¹ Laboratory of Chemical Pharmacology, National Heart Institute, National Institutes of Health, Bethesda, Maryland 20014

When ouabain and labeled serotonin (¹⁴C-5-HT) or norepinephrine (³H-NE) are simultaneously introduced into a suspension of isolated nerve endings (synaptosomes) in Krebsbicarbonate solution, the initial accumulation of ³H-NE by the synaptosomes proceeds for a few minutes, then abruptly stops. When ouabain is first incubated with synaptosomes in the absence of substrate, the initial accumulation of ¹⁴C-5-HT subsequently added is blocked. Thus, a lapse of time is required for the inhibitory effect of ouabain to develop. Moreover, Na⁺ must also be present with the ouabain. In contrast, ouabain inhibits (Na⁺ + K⁺)-ATPase activity immediately. It appears, therefore, that ouabain blocks the accumulation of amine by an indirect process resulting from the inhibition of (Na⁺ + K⁺)-ATPase. The indirect process requires Na⁺ and is probably the increase in the intracellular Na⁺ concentration which occurs in the presence of ouabain.