Journal of Neuroscience, Vol 10, 1654-1663, Copyright © 1990 by Society for Neuroscience
Properties of non-NMDA excitatory amino acid-activated channels in isolated retinal horizontal cells
EM Lasater
University of Utah, School of Medicine, Department of Physiology 84108.
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.