Molecular cloning and functional analysis of recombinantly expressed ionotropic glutamate receptors (GluR) have revealed a large variety of GluR subunits that could be grouped into three families: AMPA, kainate and NMDA receptors. Different kinetic and ion permeation properties of the channels formed from GluR subunits were obtained using human embryonic kidney 293 cells as an expression system and fast agonist application combined with whole-cell current recording. Common structural elements responsible for ion permeation through recombinant GluR channels are identified by point mutation analysis. These data may provide a guideline for the identification of the molecular composition of native GluR channels on the basis of both their functional properties and the expression pattern of their subunits.