Na+,K+-ATPase interaction with a brain endogenous inhibitor (endobain E).
Na+,K+-ATPase activity of rat brain synaptosomal membranes was evaluated in the presence of an inhibitory fraction II-E (termed endobain E), isolated by gel filtration and anionic exchange HPLC of a rat brain soluble fraction. We studied endobain E aging, analyzed its inhibitory potency in the absence or presence of ouabain as well as its ability to block high affinity [3H]ouabain binding to cerebral cortex membranes. Similar loss of endobain E activity was observed when samples were stored either dried or in solution. Endobain E fraction inhibited synaptosomal membrane Na+,K+-ATPase activity in a concentration-dependent manner and the slope of the corresponding curve strongly resembled that of ouabain. Assays performed in the presence of endobain E and ouabain indicated that the inhibitory effect was additive or less than additive, depending on their respective concentrations during preincubation and/or incubation. High affinity [3H]ouabain binding to cerebral cortex membranes proved concentration-dependent from 0.10 to 0.50 mg protein per ml; binding inhibition by endobain E was independent of protein concentration within the above range. [3H]ouabain binding inhibition by endobain E was concentration-dependent over a 10-fold range, an effect similar to that found for Na+,K+-ATPase inhibition. The extent of endobain E effect on Na+,K+-ATPase inhibition was much higher (90-100%) than that on [3H]ouabain binding blockade (50%). Findings suggest some type of interaction between endobain E and ouabain inhibitory mechanisms and favour the view that the former behaves as an endogenous ouabain.
Rodríguez de Lores Arnaiz
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Instituto de Biología Celular y Neurociencias Prof. Eduardo De Robertis, Facultad de Medicina, Universidad de Buenos Aires, Argentina. grodrig@ffyb.uba.ar
Reinés
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Herbin
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Peña
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D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism*; D008297:Male; D010042:Ouabain / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013574:Synaptosomes / Q000201:enzymology
D004791:Enzyme Inhibitors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase