Similar perisynaptic glial localization for the Na+,K+-ATPase alpha 2 subunit and the glutamate transporters GLAST and GLT-1 in the rat somatosensory cortex.
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.
Cholet
N
N
Laboratory of Cerebrovascular Research, Montreal Neurological Institute, McGill University, 3801 University Street, Montréal, Québec, Canada, H3A 2B4.
Pellerin
L
L
Magistretti
P J
PJ
Hamel
E
E
D027322:Amino Acid Transport System X-AG / Q000032:analysis* / Q000648:ultrastructure; D000818:Animals; D027342:Excitatory Amino Acid Transporter 2 / Q000032:analysis* / Q000648:ultrastructure; D008297:Male; D009457:Neuroglia / Q000737:chemistry* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis* / Q000648:ultrastructure; D013003:Somatosensory Cortex / Q000737:chemistry* / Q000648:ultrastructure; D013569:Synapses / Q000737:chemistry* / Q000648:ultrastructure
D027322:Amino Acid Transport System X-AG; D027342:Excitatory Amino Acid Transporter 2; D000254:Sodium-Potassium-Exchanging ATPase