Effect of Na+, K(+)-ATPase modifiers on high-affinity ouabain binding determined by quantitative autoradiography

There is growing evidence on the existence of endogenous ouabain-like factors that modulate Na+, K(+)-ATPase activity. In this laboratory, two soluble subfractions (peaks I and II) were previously separated from rat cerebral cortex, which had opposite effects on Na+, K(+)-ATPase activity. Peak I stimulated and peak II inhibited the enzyme (Rodríguez de Lores Arnaiz and Antonelli de Gómez de Lima, Neurochem Res 11:933-947, 1986). The same effects are now reported for K(+)-p-nitrophenyphosphatase activity. Localization of high-affinity ouabain binding in rat brain was done by quantitative autoradiography using a microcomputer digital imaging system. Peak I did not modify, whereas peak II blocked ouabain binding in areas 3-4 of cerebral cortex, dentate gyrus, stria terminalis, thalamic nuclei, and basal ganglia. Similar results were obtained when ouabain binding was determined in rabbit cerebral cortex and by a conventional filtration assay in nerve ending membranes obtained from rat cerebral cortex. These results favour the idea that the factor present in peak II fraction might behave as an ouabain-like substance.