Possible roles of AMPA/KA receptor in cultured Müller cells.

In order to identify the function of the AMPA/KA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate) receptor in cultured Müller cells, we studied the difference in the affinity of this receptor for cultured Müller cells and retinal neurons (neurons), comparing these to the characteristics of cultured Müller cells exposed to kainate (KA), a neurotoxic amino acid. The difference in the cellular responses of Müller cells and neurons to AMPA was evaluated by measuring the rapid change in intracellular calcium ions. Results showed that neurons were more sensitive to AMPA than Müller cells; the percentage of cells responding to AMPA was always higher for neurons. When Müller cells were exposed to 0.5 mM KA, the morphology of the cells was not affected and the concentration of lactate dehydrogenase in the culture solution did not increase. However, the percentage of cells responding to a high concentration of AMPA was higher in the Müller cells exposed to KA than in those not exposed. These findings indicated that the affinity of the AMPA receptor was lower in Müller cells than in neurons, and that Müller cells were resistant to neurotoxic amino acids. It was also suggested that when an extremely large amount of neurotoxic amino acid was released into the retina as a result of ischemia, Müller cells actively protected the neurons.