Glycine transporters are differentially expressed among CNS cells.
Glycine is the major inhibitory neurotransmitter in the spinal cord and brainstem and is also required for the activation of NMDA receptors. The extracellular concentration of this neuroactive amino acid is regulated by at least two glycine transporters (GLYT1 and GLYT2). To study the localization and properties of these proteins, sequence-specific antibodies against the cloned glycine transporters have been raised. Immunoblots show that the 50-70 kDa band corresponding to GLYT1 is expressed at the highest concentrations in the spinal cord, brainstem, diencephalon, and retina, and, in a lesser degree, to the olfactory bulb and brain hemispheres, whereas it is not detected in peripheral tissues. Pre-embedding light and electron microscopic immunocytochemistry show that GLYT1 is expressed in glial cells around both glycinergic and nonglycinergic neurons except in the retina, where it is expressed by amacrine neurons, but not by glia. The expression of a 90-110 kDa band corresponding to GLYT2 is restricted to the spinal cord, brain-stem, and cerebellum; in addition, very low levels occur in the diencephalon. GLYT2 is found in presynaptic elements of neurons thought to be glycinergic. However, in the cerebellum, GLYT2 is expressed both in terminal boutons and in glial elements. The physiological consequences of the regional and cellular distributions of these two proteins as well as the possibility of the existence of an unidentified neuronal form of GLYT1 are discussed.
Zafra
F
F
Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain.
Aragón
C
C
Olivares
L
L
Danbolt
N C
NC
Giménez
C
C
Storm-Mathisen
J
J
D000595:Amino Acid Sequence; D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D001933:Brain Stem / Q000378:metabolism; D002352:Carrier Proteins / Q000032:analysis / Q000096:biosynthesis* / Q000737:chemistry; D003001:Cloning, Molecular; D017931:DNA Primers; D004027:Diencephalon / Q000378:metabolism; D015870:Gene Expression; D005998:Glycine / Q000378:metabolism; D050487:Glycine Plasma Membrane Transport Proteins; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D009457:Neuroglia / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009830:Olfactory Bulb / Q000378:metabolism; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012160:Retina / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism
D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D017931:DNA Primers; D050487:Glycine Plasma Membrane Transport Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C493269:Slc6a5 protein, rat; C493266:Slc6a9 protein, rat; D005998:Glycine