Receptors Are Expressed in Cone-Driven Horizontal Cells in Carp Retina

Glutamate works as a major excitatory neurotransmitter in the vertebrate retina. Whole-cell recordings made from isolated carp cone horizontal cells (H1 cells) showed that Nmethyl-D-aspartate (NMDA), co-applied with glycine, induced inward currents that were blocked by the NMDA receptor competitive antagonist D -2-amino-5-phosphonopentanoate ( D -AP5) and 5,7-dichlorokynurenic acid (DCKA), a selective NMDA receptor antagonist acting at the glycine site on the NMDA receptor complex. Moreover, calcium imaging showed that NMDA caused a significant elevation of intracellular calcium levels ([Ca 2+ ] i ) of H1 cells, which was also blocked by D -AP5. In contrast, neither inward currents nor changes in [Ca 2+ ] i could be induced by NMDA in rod horizontal cells (H4 cells). Intracellular recordings made from H1 cells in the isolated retina, superfused with Ringer’s containing 1 m M Mg 2+ , in the dark demonstrated that NMDA reduced the light-off overshoot of H1 cells. We therefore conclude that the functional NMDA receptor is expressed in carp H1 cells, from which this receptor has been thought to be absent, and this receptor may play a role in modulating cone-driven signal of horizontal cells in the dark. Copyright © 2006 S. Karger AG, Basel Received: June 13, 2006 Accepted after revision: July 7, 2006 Published online: October 17, 2006 Dr. Xiong-Li Yang Institute of Neurobiology, Fudan University 138 Yixueyuan Road Shanghai, 200032 (China) Tel. +86 21 6422 1975, Fax +86 21 5423 7647, E-Mail [email protected] © 2006 S. Karger AG, Basel 1424–862X/06/0154–0174$23.50/0 Accessible online at: www.karger.com/nsg D ow nl oa de d by : 54 .1 91 .4 0. 80 4 /1 8/ 20 17 9 :1 4: 17 P M