POSSIBLE ROLES OF AMPA KA RECEPTOR IN CULTURED MULLER CELLS/

In order to identify the function of the AMPA/KA (alpha-amino-3-hydrox y-5-methyl-4-isoxazole propionate/kainate) receptor in cultured Muller cells, we studied the difference in the affinity of this receptor for cultured Muller cells and retinal neurons (neurons), comparing these to the characteristics of cultured Muller cells exposed to kainate (KA ), a neurotoxic amino acid. The difference in the cellular responses o f Muller cells and neurons to AMPA was evaluated by measuring the rapi d change in intracellular calcium ions. Results showed that neurons we re more sensitive to AMPA than Muller cells; the percentage of cells r esponding to AMPA was always higher for neurons. When Muller cells wer e exposed to 0.5 mM KA, the morphology of the cells was not affected a nd the concentration of lactate dehydrogenase in the culture solution did not increase. However, the percentage of cells responding to a hig h concentration of AMPA was higher in the Muller cells exposed to KA t han in those not exposed. These findings indicated that the affinity o f the AMPA receptor was lower in Muller cells than in neurons, and tha t Muller cells were resistant to neurotoxic amino acids. It was also s uggested that when an extremely large amount of neurotoxic amino acid was released into the retina as a result of ischemia, Muller cells act ively protected the neurons.