Characteristics of single-channels activated by quisqualate and kainate in teleost retinal horizontal cells.

There is increasing evidence in the teleost retina that the excitatory amino acid glutamate is the neurotransmitter used by some photoreceptors. Single kainate and quisqualate channels were recorded on isolated white bass horizontal cells using patch-clamp techniques. Two categories of channels were observed. The first, labelled a slow-channel, exhibited conductance and open time averages for channels activated by quisqualate of 8.5 pS and 8.8 msec, and for kainate 8.5 pS and 4.5 msec. The closed times of these channels could be described by two time constants. The second channel category was termed a fast-channel. Quisqualate and kainate activated channels in this category with two prominent conductances in the range of about 10 pS and 20-30 pS and open times of 1-2 msec. These channels demonstrated closed times with only a single time constant. Openings of slow-channels elicited by the agonists tended to occur in bursts. Activity of the fast-channels was noisy and no bursting behavior could be seen. Both channels exhibited multiple conductance states.