RESUMO
The presence of kainic (KA) and quisqualic acid (QA) receptors on inner retinal neurones of the axolotl Ambystoma mexicanum has been studied using intracellular recording techniques. In the presence of CoCl2, which blocks neurotransmitter release, KA and QA depolarized the membrane. The minimum concentration of KA that induced a response was 1 microM and a maximum response was obtained with 10 microM (EC50: 3 microM). The operating range of QA was between 0.5 and 5 microM with an EC50 of 1 microM. These data show that inner retinal cells of the axolotl are sensitive to KA and QA. Cis-2,3-piperidine dicarboxylic acid (PDA, 3 mM) completely blocked responses to 5 microM KA, but not those induced by 2 microM QA. This suggests that the KA- and QA-sensitive receptors on inner retinal cells of the salamander are pharmacologically different and that PDA can be a valuable tool in distinguishing KA- and QA-sensitive receptors on these neurones.