Glutamate receptor currents were examined in horizontal cells from
cultured human retina using whole-cell recording procedures. Horizontal
cells possess both AMPA and kainate receptors and both produce
significant sustained currents. The kainate-induced current did not
show significant desensitization and was not enhanced by concanavalin
A. The sustained AMPA current was smaller than the kainate current, but
the difference was almost entirely due to pronounced desensitization.
The horizontal cell AMPA current was enhanced by cyclothiazide but not
by PEPA, indicating the presence of the flip receptor variant.
GYKI-52466 blocked the AMPA response (IC50 = 5
μM against 100 μM AMPA) but also blocked the kainate response
(IC50 = 45 μM against 100 μM kainate). The
diversity of glutamate receptors in human horizontal cells suggests
that synaptic input to these neurons may be multiplexed through both
kainate and AMPA channels.