Our data (Table 1) have been used to calculate the GLAST and GLT concentrations both per volume of tissue and per cell membrane area. For the calculations presented in this table, it is assumed that brain tissue contains ∼97.8 gm/kg protein (Lowry et al., 1954) and has a density of 1.05 gm/cm³ (Lowry, 1953) (i.e. 1 μm³ contains ∼10⁻¹³ gm of protein) and that the molecular masses of the polypeptide parts of GLAST (Storck et al., 1992) and GLT (Pines et al., 1992) are 61 and 64 kDa, respectively. The total plasma membrane density was ∼14 μm²/μm³ in both regions.

↵F2-a Astroglial membrane. The protein is almost exclusively present in astrocytic membranes (Chaudhry et al., 1995;Lehre et al., 1995).

↵F2-b Data from Dehnes et al. (1998).

↵F2-c Purkinje cell spine membrane. NB: It must be kept in mind that these are average values (Dehnes et al., 1998). First, EAAT4 is exclusively expressed in Purkinje cells but is unevenly distributed in the membranes of the individual Purkinje cell. The highest concentrations are found in the parts of the membrane facing glia. Second, EAAT4 is also unevenly distributed in the molecular layer, and it is expressed at different densities in different parasagittal zones. The values given here are based on a large part of the molecular layer (including both weakly and strongly expressing zones) and represent the average densities in the Purkinje cell spine membrane facing glia. The densities in the weakly and strongly expressing zones are not known but are assumed (Dehnes et al., 1998) to be approximately two times lower or higher, respectively, than the average value.