Gb. Grant et Fs. Werblin, A GLUTAMATE-ELICITED CHLORIDE CURRENT WITH TRANSPORTER-LIKE PROPERTIES IN ROD PHOTORECEPTORS OF THE TIGER SALAMANDER, Visual neuroscience, 13(1), 1996, pp. 135-144
Glutamate, when puffed near the synaptic terminals, elicits a current
in rod photoreceptors. The current is strongly dependent upon both the
intracellular and extracellular chloride concentration: its reversal
potential follows the predicted Nernst potential for a chloride permea
ble channel. The glutamate-elicited current also requires the presence
of extracellular sodium. This glutamate-elicited current is pharmacol
ogically like a glutamate transporter: it is elicited, in order of eff
icacy, by L-glutamate, L-aspartate, L-cysteate, D-aspartate, and D-glu
tamate, all shown to activate glutamate transport in other systems. Fu
rthermore, it is reduced by the glutamate transport antagonists dihydr
okainate (DHKA) and D,L-threo-3-hydroxyaspartate (THA). THA, when appl
ied alone, elicits a current similar to that elicited by glutamate. Th
e current cannot be activated by the glutamate receptor agonists kaina
te, quisqualate, NMDA and APB, nor can it be blocked by the glutamate
receptor antagonists CNQX and APV. Thus, the current does not appear t
o be mediated by a conventional glutamate receptor. Taken together, th
e ionic dependence and pharmacology of this current suggest that it is
generated by glutamate transporter coupled to a chloride channel.