Selective antagonism of rat inhibitory glycine receptor subunits

Retinal ganglion cells exhibit fast and slow inhibitory synaptic glycine currents that can be selectively inhibited by strychnine and 5,7-dichlorokynurenic acid (DCKA), respectively. In this study we examined whether strychnine and DCKA selectivity correlated with the subunit composition of the glycine receptor. Homomeric α1, α2 or α2* glycine subunits were in vitro expressed in human embryonic kidney cells (HEK 293). In cells expressing the α1 subunit, responses to 200 μM glycine were blocked by 1 μM strychnine but not by 500 μM DCKA. In cells expressing the α2 subunit, both 1 μM strychnine and 500 μM DCKA were effective antagonists of 200 μM glycine. In cells expressing α2* subunits, which are much less glycine-sensitive, 10 mM glycine was inhibited by 500 μM DCKA but not by 1 μM strychnine. A single amino acid mutation in the α1 subunit (R196G), converted this subunit from DCKA-insensitive to DCKA-sensitive. In conclusion, the comparative effectiveness of strychnine and DCKA can be used to distinguish between the α1, α2 and α2* receptor responses. Furthermore, a single amino acid near the glycine receptor's putative agonist binding site may account for differences in DCKA sensitivity amongst the α subunits.