Ishiuchi et al. studied Ca2+ permeable AMPA receptors in GBM cells, and stated, that due to the lack of the GluR2 subunit in GBM cells, these glutamate receptors had become Ca2+ permeable, emphasizing that GluR1 and GluR4 subunits are ubiquitously expressed in human GBM cells. This evidence concerns the gene GRIA4 and glioblastoma.