Changes in the Distribution of theα3 Na+/K+ATPase Subunit in Heterozygous Lurcher Purkinje Cells as a Genetic Model of Chronic Depolarization during Development

Jean Mariani,Hadi S Zanjani,Michael W Vogel,Rebecca Mcfarland

doi:10.1155/2014/152645

Abstract

A common assumption of excitotoxic mechanisms in the nervous system is that the ionic imbalance resulting from overstimulation of glutamate receptors and increased Na+ and Ca++ influx overwhelms cellular energy metabolic systems leading to cell death. The goal of this study was to examine how a chronic Na+ channel leak current in developing Purkinje cells in the heterozygous Lurcher mutant (+/Lc) affects the expression and distribution of the α3 subunit of the Na+/K+ ATPase pump, a key component of the homeostasis system that maintains ionic equilibrium in neurons. The expression pattern of the catalytic α3 Na+/K+ ATPase subunit was analyzed by immunohistochemistry, histochemistry, and Western Blots in wild type (WT) and +/Lc cerebella at postnatal days P10, P15, and P25 to determine if there are changes in the distribution of active Na+/K+ ATPase subunits in degenerating Purkinje cells. The results suggest that the expression of the catalytic α3 subunit is altered in chronically depolarized +/Lc Purkinje cells, although the density of active Na+/K+ ATPase pumps is not significantly altered compared with WT in the cerebellar cortex at P15, and then declines from P15 to P25 in the +/Lc cerebellum as the +/Lc Purkinje cells degenerate.

Highlights

The Na+/K+ ATPase pump (Na/K pump) in neurons plays a key role in maintaining the transmembrane electrical gradient that is critical for normal function
In both wild type (WT) and +/Lc cerebella from P10 to P25, the α3 subunits appear to be expressed in Purkinje cells, the molecular layer, and granule cell layer glomeruli in a similar pattern to that described by Peng et al [7] in the cerebellum of adult rats. α3 expression in WT Purkinje cells is diffusely distributed throughout the dendrites and cell body as shown for P15 WT Purkinje cells in Figures 1(b) and 1(c)
The α3 labeling is intense in the two left most +/Lc Purkinje cells in Figures 1(d)–1(f), where the α3 isoform appears to surround the stunted primary Purkinje cell dendrites especially in the lower two-thirds of the molecular layer. α3 immunolabeling is seen around the Purkinje cell bodies but not as much within the cell body in comparison with WT Purkinje cells. α3 immunolabeling in the granule cell layer glomeruli is indicated by white asterisks in Figures 1(e) and 1(f)

Summary

Introduction

The Na+/K+ ATPase pump (Na/K pump) in neurons plays a key role in maintaining the transmembrane electrical gradient that is critical for normal function. The mature pump resides in the plasma membrane and exports 3 Na+ ions for every two K+ ions it imports at a cost of 1 ATP molecule, resulting in a net outward, hyperpolarizing current [1]. All Na/K pumps contain an alpha (α) and a beta (β) unit, though in some cell types the pump contains an additional FXYD protein [4, 5]. The β subunit plays a crucial role in the structure and maturation of the Na/K pump, including, for example, aiding in the tracking of the α subunit from the ER to the plasma membrane [6]. Cerebellar Purkinje cells exclusively express the α3 and β1 subunits, but some other cerebellar neurons (e.g., basket cells) or structures (e.g., granule cell layer glomeruli) express the α3 subunit [7]. The FXYD family protein, FXYD1 (Phospholemman), is expressed in Purkinje cells and the molecular layer of the cerebellum [8], but this protein was not analyzed in this study

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