Ouabain-induced isoform-specific localization change of the Na+, K+-ATPase α subunit in the synaptic plasma membrane of rat brain

Na+, K+-ATPase is one of major membrane proteins that has two subunits, α and β. The α subunit has the ATPase activity and the ouabain binding site. Among four isoforms of the α subunit, expression of α1, α2, and α3, but not α4, is observed in matured rat brain. Ouabain is one of cardiac glycosides, and endogenous ouabain-like compounds have been recognized as a new class of steroid hormone. The α subunit is considered as their endogenous receptor. Recent studies envisaged the importance of membrane microdomains (MDs) as signaling platforms, which are recovered as a detergent-resistant membrane microdomain fraction (DRM). Although this ATPase has been considered as a non-DRM protein, some amount of the α subunit was found to be a component of the DRM prepared from the synaptic plasma membrane fraction (SPM) of rat brain. Ouabain treatment increased the amount of α3 isoform, but not α1, in the DRM derived from synaptosome fraction and SPM. These results suggest that the localization of the α subunit of Na+, K+-ATPase is regulated with isoform-specific mechanisms and the physiological importance of DRM in the signal transduction of the endogenous ouabain-like steroid hormone in neurons.