GLAST protein

Neuronal expression of GLAST protein has not been detected anywhere in the nervous system in vivo, neither in the adult nor during development, although a possible expression of GLAST mRNA in granule cells of the mouse hippocampus (gyrus dentatus) at birth (PO) has been described (Sutherland et al., 1996), but this has not been verified with antibodies. However, it has recently been reported that GLAST protein is transiently expressed in a subpopulation of cultured embryonic hippocampal neurons (Plachez et ah, 2000). 

The rule applies to retina as well GLAST is present in both Muller cells and in regular astrocytes (Derouiche and Rauen, 1995 Derouiche, 1996 Rauen et ah, 1996, 1998 Lehre et ah, 1997). 

It has been debated if GLAST is expressed in the retinal pigment epithelium and in oligodendrocytes. Expression has been reported by some (Derouiche and Rauen, 1995 Choi and Chiu, 1997 Domercq and Mature, 1999 Domercq et ah, 1999), but questioned by others (Lehre et ah, 1995, 1997 Schmitt et ah, 1997). Finally, GLAST is present in fibrocytes and in supporting cells of inner ear (Furness and Lehre, 1997 Takumi et ah, 1997). 

The highest concentrations of GLAST are seen in the molecular layer of the cerebellum, the Bergmann glia in particular (Lehre et ah, 1995). Compared to the cerebellum, the concentrations of GLAST protein in bulbus olfactorius, hippocampus, cerebral cortex and thalamus are 49, 35, 33 and 22%, respectively (Lehre et ah, 1995 Lehre and Danbolt, 1998 0. Haugeto and N.C. Danbolt, unpublished). 

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Direct phosphorylation of the glutamate transporter proteins themselves has only been reported for GLT and GLAST. Protein kinase C phosphorylates GLAST and thereby reduces the transport activity to 25% with no change in cell surface expression (Conradt and Stoffel, 1997). GLT was originally reported to be stimulated by phosphorylation of serine-113 (Casado et al., 1993), but a recent report (Tan et al., 1999) suggests that the protein kinase-C-mediated stimulation represents an effect of the expression system used rather than an effect on GLT. Further studies are required to sort out the controversy. 

Chan H, Hazell AS, Desjardins P, Butterworth RF. Effects of ammonia on glutamate transporter (GLAST) protein and mRNA in cultured rat cortical astrocytes. Neurochem. Int., 37,243—248, 2000... 

Lehre KP, Davanger S, Danbolt NC (1997) Localization of the glutamate transporter protein GLAST in rat retina. Brain Res 744 129-151. 

Ullensvang K, Lehre KP, Storm-Mathisen J, Danbolt NC (1997) Differential developmental expression of the two rat brain glutamate transporter proteins GLAST and GLT. Eur J Neurosci 9 1646-1655. 

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