A Specific and Essential Role for Na,K-ATPase α3 in Neurons Co-expressing α1 and α3

Most neurons co-express two catalytic isoforms of Na,K-ATPase, the ubiquitous α1, and the more selectively expressed α3. Although neurological syndromes are associated with α3 mutations, the specific role of this isoform is not completely understood. Here, we used electrophysiological and Na + imaging techniques to study the role of α3 in central nervous system neurons expressing both isoforms. Under basal conditions, selective inhibition of α3 using a low concentration of the cardiac glycoside, ouabain, resulted in a modest increase in intracellular Na + concentration ([Na + ] i ) accompanied by membrane potential depolarization. When neurons were challenged with a large rapid increase in [Na + ] i , similar to what could be expected following suprathreshold neuronal activity, selective inhibition of α3 almost completely abolished the capacity to restore [Na + ] i in soma and dendrite. Recordings of Na,K-ATPase specific current supported the notion that when [Na + ] i is elevated in the neuron, α3 is the predominant isoform responsible for rapid extrusion of Na + . Low concentrations of ouabain were also found to disrupt cortical network oscillations, providing further support for the importance of α3 function in the central nervous system. The α isoforms express a well conserved protein kinase A consensus site, which is structurally associated with an Na + binding site. Following activation of protein kinase A, both the α3-dependent current and restoration of dendritic [Na + ] i were significantly attenuated, indicating that α3 is a target for phosphorylation and may participate in short term regulation of neuronal function. Background: Neurons express two Na,K-ATPase isoforms, the ubiquitous α1 and neuron-specific α3. Results: α3 is important for control of membrane potential and is fully responsible for restoration of large [Na + ] i increases. Conclusion: α1 and α3 are required for basal neuronal function, but α3 controls restoration of [Na + ] i following sustained discharge. Significance: Conditions associated with defect α3 function are likely aggravated by suprathreshold neuronal activity.