On the sensitivity of H1 horizontal cells of the carp retina to glutamate, aspartate and their agonists.

Threshold concentrations for L-glutamate, L-aspartate and their agonists, kainate, quisqualate and N-methyl-D,L-aspartate, were determined for horizontal cells of the intact carp retina and horizontal cells that were enzymatically isolated and maintained in culture. Our results indicate that uptake or other mechanisms decrease the apparent sensitivity of these cells in the intact retina to L-glutamate by 25-200 times. Our findings also suggest that L-glutamate is more likely a photoreceptor transmitter than L-aspartate.