Properties of non-NMDA excitatory amino acid-activated channels in isolated retinal horizontal cells

The excitatory amino acid glutamate is believed to be the neurotransmitter used by some photoreceptors in the teleost retina. Past studies have shown that exogenous glutamate, and its analogs, are capable of affecting second-order retinal neurons in a manner consistent with the action of a photoreceptor transmitter. In an effort to characterize the properties of retinal glutamate channels on second-order neurons, non-NMDA excitatory amino acid-activated channels were studied in single horizontal cells isolated from the retina of the white bass. Using patch-clamp techniques single glutamate, kainate, and quisqualate channels were recorded. Two categories of channels were observed. The first was labeled slow-channels. Single-channel conductances and open times for this channel showed a range of values, but the average for channels activated by glutamate was 12 pS and 5.6 msec; quisqualate, 8.5 pS and 8.8 msec; and kainate, 8.5 pS and 4.5 msec. Openings of slow-channels elicited by the agonists tended to occur in bursts with a mean burst length of 38 msec. The bursts were punctuated by numerous, brief closings. The second channel category was termed fast channels. The agents glutamate, quisqualate, and kainate all activated channels in this category with open times of 1-2 msec and 2 prominent conductances in the range of about 10 and 20-30 pS. Activity of the fast channels tended to be noisy and no bursting behavior was observed.