Two distinct types of AMPA responses in cultured rat hippocampal neurons.

We previously found two distinct types of responses to kainate in cultured rat hippocampal neurons. The type I response is characterized by very little increase in Ca2+ permeability with an outward rectification in the current-voltage (I-V) relation of the kainate response. In contrast, the type II kainate response is characterized by prominent Ca2+ permeability and an inward rectification. These two types of responses were mimicked by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA). Furthermore, AMPA cross-desensitized both types of kainate responses. These results indicate that two functionally different types of AMPA/kainate receptors are expressed in hippocampal neurons.