The Na⁺,K⁺-ATPase is the membrane bound enzyme that maintains the K⁺ and Na⁺ intracellular gradients used in the nervous system (NS) by other proteins for electrical membrane potential changes and uptake of neurotransmitters. In astrocytes, it participates in the uptake of K⁺ after depolarization of neurons. The system consists of two subunits: the α subunit (112 kDa) and the β subunit (a 45 kDa glycoprotein). The α has four different isoforms. In brain, α2 predominates in astrocytes and α3 in neurons, and α1 is ubiquitous. The β subunit has also four different isoforms. β3 in the NS is only expressed in photoreceptors and oligodendrocytes. All αβ combinations may exist and the patterns of subcellular and developmental specification are extremely complex. Also control of biosynthesis and the enzyme properties, such as ion affinities, are affected by the choice of α and β. The aim of this study was to determine the cellular redistribution of Na⁺,K⁺-ATPase subunit isoforms after injury of the sciatic nerve of the rat. We performed double-labelling (ATPase/cell-specific markers) immunofluorescence in frozen sections of dorsal root ganglia (DRG) of the regenerating tissue using isoform-specific antibodies. Samples were collected from Sprague-Dawley rats after sciatic nerve transection and reconstruction into a Silastic chamber 1.47 mm diameter under ketamine anaesthesia, in both cases: during surgery and during sample collecting. Once samples were collected, animals were killed by overdosage of anaesthesic.

We have found that α1 and α2 immunoreactivities in normal DRG are similar in intensity and localization in the plasma membrane of all kinds of cells, with no signal for α3 isoform. After injury α1 and α2 expression decreases evenly in all cells and there is a remarkable onset in the expression of α3, with a peak about day three and it gradually disappears during regeneration.

Regarding β subunits isoforms, β1 immunoreactivity is restricted to a perinuclear halo of neurons, with no dependence on the kind or shape of neurons, and to the cytoplasm of the small glial cells surrounding these neurons. No β2 was found. β3 specific immunofluorescence is most abundant in the cytoplasm of small neurons and much less abundant in big and medium size neurons.

Suddenly after injury, β1 shows a homogeneous distribution in the soma of neurons. As regeneration proceeds, this isoform recovers its original emplacement around the nucleus, although a faint signal still remains all over the cytosol.

The β3-specific immunolabelling signal in small neurons progressively decays after injury until day 3, then the signal increases in intensity, becoming stronger than previous to injury at day 7 then progressively decreases to normal levels.

The diversity of Na⁺,K⁺-ATPase subunit isoforms and their complex cellular, spatial and temporal patterns of cellular expression in the DRG suggest that Na⁺,K⁺-ATPase isozymes perform specialized physiological functions during regeneration.