NMDA modulation of GABA transporter current in carp retinal horizontal cells

In the present study, the modulatory effect of NMDA on GABA transporter current was investigated on enzymatically isolated horizontal cells of carp retina. After application of NMDA (0.1 mM) for 50 s, the GABA transporter current elicited by GABA (1 mM) was decreased to 78.07 ± 3.10% (n = 5) of the control level. When the extracellular Ca2+ was removed from the Ringer's solution, the NMDA inhibitory effect on the GABA transporter current was eliminated. The suppression effect could be attenuated when the Ca2+ release and Ca2+ uptake of intracellular Ca2+ store were blocked after the cell had been pre-incubated with 20 μM ryanodine plus 2 μM thapsigargin. Application of 10 mM BAPTA in intracellular solution also suppressed the NMDA modulation of GABA transporters. These results suggest that the activation of NMDA receptors inhibits GABA transporter-mediated current by affecting Ca2+ processes in the retinal horizontal cells.