The activation mechanism of Na,K-ATPase in nerve fibres after rhythmic excitation was studied. 3H-ouabain binding to a nerve was found to depend on the frequency of rhythmic excitation. The maximum of 3H-ouabain binding to a nerve crab was at 10 imp/sec. Rhythmic excitation was found not to change Na,K-ATPase affinity to ouabain, but appeared to increase the concentration of ouabain-sensitive sites in the nerve membrane. Transformation of inactive forms of the enzyme into active ones was supposed to be a possible cause of greater 3H-ouabain binding to the nerve during rhythmic exitation.
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