Similar Perisynaptic Glial Localization for the Na+,K+-ATPase alpha2 Subunit and the Glutamate Transporters GLAST and GLT-1 in the Rat Somatosensory Cortex

Abstract

Several isoenzymes of the Na(+),K(+)-ATPase are expressed in brain but their specific roles are poorly understood. Recently, it was suggested that an isoenzyme of the Na(+),K(+)-ATPase containing the alpha(2) subunit, together with the glutamate transporters GLAST and GLT-1, participate in a coupling mechanism between neuronal activity and energy metabolism taking place in astrocytes. To substantiate this hypothesis, we compared the distribution of alpha(2), GLAST and/or GLT-1 in the rat cerebral cortex using double immunofluorescence and confocal microscopy, and immunocytochemistry at the electron microscopic level. We also investigated the relationship between alpha(2), GLAST or GLT-1 and asymmetrical synaptic junctions (largely glutamatergic) and GABAergic nerve terminals. Results show that the alpha(2) subunit has an exclusive astroglial localization, and that it is almost completely co-distributed with GLAST and GLT-1 when evaluated by confocal microscopy. This similar distribution was confirmed at the ultrastructural level, which further showed that the vast majority of the alpha(2) staining (73% of all labelled elements), like that of GLAST and GLT-1, was located in glial leaflets surrounding dendritic spines and the dendritic and/or axonal elements of asymmetrical (glutamatergic) axo-dendritic synapses. Synapses ensheathed by alpha(2), GLAST or GLT-1 virtually never included (<or=2%) GABAergic nerve terminals or synaptic junctions. However, a subset of GABAergic nerve terminals (10-14%) were directly apposed to asymmetrical axo-dendritic junctions surrounded by alpha(2), GLAST or GLT-1. Altogether these results demonstrate that alpha(2), GLAST and GLT-1 have comparable perisynaptic distribution within cortical astrocytes most likely associated with glutamatergic synapses.

Familial Hemiplegic Migraine

“…82 In the adult somatosensory cortex the ␣ 2 Na ϩ ,K ϩ -ATPase isoform is located exclusively in glial cells and shows a localization virtually identical to that of the astrocytic glutamate transporters GLAST and GLUT1; at the ultrastructural level it appears preferentially localized in astrocytic processes around asymmetrical (glutamatergic) synaptic junctions, and not around GABAergic terminals. 78 These structural data and previous functional data (e.g., Pellerin and Magistretti 83 ) are consistent with a specific functional coupling of the ␣ 2 Na ϩ ,K ϩ -ATPase with astrocytic glutamate transporters and a specific role in glutamate clearance by glial cells during neuronal activity in the adult cortex.…”

“…75 In the murine brain, the ␣ 2 Na ϩ ,K ϩ -ATPase is expressed primarily in neurons during embryonic development and at the time of birth, and primarily in glial cells in the adult. [76][77][78] Impaired clearance of neurotransmitters and enhanced neuronal excitation in the amygdala and pyriform cortex were shown in Atp1a2 Ϫ/Ϫ mice at the embryonic stage. 79 These mice die at birth because of lack of spontaneous respiratory activity due to functional impairment of the brainstem respiratory neurons, probably as a result of elevated intracellular [Cl Ϫ ] that would switch the GABA response from hyperpolarization to depolarization; the data suggest a specific coupling between the ␣ 2 Na ϩ ,K ϩ -ATPase and the neuron-specific K ϩ -Cl Ϫ cotransporter, which excludes Cl Ϫ ions from the cytosol in respiratory center neurons.…”

Ex Vivo Analysis of Lactate and Glucose Metabolism in the Rat Brain under Different States of Depressed Activity

“…Time dependence of lactate C3 and alanine C3 enrichments in rat brain after blood circulation arrest. The rats treated with either pentobarbital (A), ␣-chloralose (B), or morphine (C) were infused with a solution of 750 mM [1][2][3][4][5][6][7][8][9][10][11][12][13] C]glucose plus 500 mM lactate. Time zero was defined as the instant when their cranium was split in two parts to remove brain hemispheres.…”

“…The proposed astrocyte-neuron lactate shuttle hypothesis (ANLSH) 1 (1) as the coupling model between neuronal activity and energy metabolism requires the involvement of different components, the occurrence and localization of which have been investigated analytically at the molecular level, i.e. glutamate transporter and Na ϩ ,K ϩ -ATPase (11), lactate dehydrogenase isoenzymes (12), and monocarboxylate transporters (13,14). Although brain lactate production and lactate use by neurons as an energy source are widely admitted, the relevance of the coupling model, particularly the neuronal utilization of glia-produced lactate, is a topical issue (15,16).…”

MONaKA, a Novel Modulator of the Plasma Membrane Na,K-ATPase

“…Elevated extracellular potassium, in turn, can cause membrane depolarization, leading to excitotoxicity as a result of the excessive release of the neurotransmitter glutamate from astrocytes or synaptic terminals (Albensi and Janigro, 2003). Because potassium accumulates to high concentrations in the relatively restricted extracellular space bounded by the presynaptic and postsynaptic neuronal elements and the associated astrocyte (Cholet et al, 2002), this may be a particularly acute problem at CNS synapses. It has long been thought that the strategic location of astrocytes allows them to play a critical role in potassium homeostasis at the synapse (Hertz, 1978) via activation of their prominent Na,K-ATPase as well as other mechanisms (Amedee et al, 1997).…”