Ionotropic glutamate receptor that functions as a cation- permeable ligand-gated ion channel. Cannot form functional channels on its own (PubMed:8263508). Shows channel activity only in heteromeric assembly with GRIK1, GRIK2 and GRIK3 subunits (By similarity). . This is the function of GRIK4 (glutamate ionotropic receptor kainate type subunit 4, Ensembl gene identifier ENSG00000149403).