A comparison of the effects of isomers of alpha-aminoadipic acid and 2-amino-4-phosphonobutyric acid on the light response of the müller glial cell and the electroretinogram.

Intracellular recordings of the light response of retinal Müller glial cells revealed differential effects of optical isomers of alpha-aminoadipic acid, a putative gliotoxin. L-alpha-aminoadipic acid preferentially abolished the "on" component but not the "off" component of the intracellularly recorded Müller cell light response, abolished the b-wave but not the d-wave of the electroretinogram, and caused histological damage to the Müller cells. D-alpha-aminoadipic acid preferentially reduced the "off" component of the Müller cell light response and the d-wave of the electroretinogram, and did not cause appreciable histological damage to the Müller cells. 2-amino-4-phosphonobutyric acid, which has been shown to act preferentially at the synapse of photoreceptors onto depolarizing bipolar cells in the mudpuppy retina, abolished the "on" response of Müller cells and the b-wave of the electroretinogram, but caused no histological damage to the Müller glial cells. None of the agents caused a significant change in the resting membrane potential of the glial cells. The similarity of the electrical effects of L-alpha-aminoadipic acid and 2-amino-4-phosphonobutyric acid suggests that the initial loss of the b-wave following L-alpha-aminoadipic acid treatment is due to action of the amino acid at a synaptic site via a mechanism distinct from that which causes subsequent histological damage to the glial cells.