Brain soluble fractions which modulate Na+, K+-ATPase activity likewise modify muscarinic receptor.

Two brain soluble fractions, named peaks I and II, which respectively stimulate and inhibit neuronal Na+, K+-ATPase activity, have been isolated by gel filtration in Sephadex G-50. Since cholinergic transmission seems related to such enzyme activity, in this study we evaluated the effect of brain peak I, peak II, a more purified fraction II-E and commercial ouabain, on specific binding of the muscarinic antagonist [3H]quinuclidinyl benzilate to membranes from rat cerebellum, hippocampus and cerebral cortex. We found that binding was increased by peak I and decreased by peak II, II-E and ouabain, all effects proving concentration-dependent. Since the changes exerted on the muscarinic receptor followed a pattern similar to the one already described for synaptosomal membrane Na+, K+-ATPase activity, both systems seem to interact at a functional level.