Properties of Mg²⁺-ATPase in Rat Brain Synaptic Plasma Membranes

Abstract

In the present study distribution and enzymatic properties of ecto-Mg2+-ATPaSe were determined in synaptic plasma membrane (SPM) preparations isolated from the hippocampus, caudate nucleus and whole brains of female rats. Western blot analysis using anti-ecto-Mg2+-ATPase antibody revealed the association of Mg2+-ATPase with SPM prepared from all the three brain sources, yet the enzyme was most abundant in caudate nucleus membranes, being 30% and 22% more abundant than in the hippocampal and whole brain tissue SPM, respectively. The evidence is also presented that kinetic properties of the brain Mg2+-ATPase are not under the control of circulating sex steroids. It was confirmed that the enzyme is activated by millimolar concentrations of Mg2+ and that it cannot be effectively inhibited by known ATPase inhibitors. The most pronounced differences in kinetic properties observed were 2.5 fold higher apparent affinity for ATP and 59% higher specific activity of Mg2+-ATPaSe of the caudate nucleus as compared with the enzyme from the hippocampus. On the other hand, the apparent enzyme affinity for Mg2+ was almost equal in all SPM preparations tested. Taken together, our results show that ecto-Mg2+-ATPase is not uniformly distributed and differs in respect to affinity for ATP in rat brain regions, thus indicating its substantial role in the process of signal transduction via controlling the levels of extracellular ATP.