NITRIC-OXIDE, 2-AMINO-4-PHOSPHONOBUTYRIC ACID AND LIGHT DARK ADAPTATION MODULATE SHORT-WAVELENGTH-SENSITIVE SYNAPTIC TRANSMISSION TO RETINAL HORIZONTAL CELLS/

Light-induced changes in the input resistance (R(in)) of external, lum inosity (i.e. H1) type horizontal cell (HC) perikarya were studied by the bridge-balance method in light-adapted and dark-adapted retinae of carp. Changes in input resistance Delta R(in) induced by short-(460 n m) and long-wavelength (674 nm) hashes, adjusted in intensity to elici t equal-amplitude membrane voltage responses (equal-voltage condition) , were measured. In light-adapted retinae, long-wavelength stimuli inc reased R(in) consistently; in contrast, the increase was much less wit h short-wavelength stimuli. This equal-voltage chromatic Delta R(in), difference was lost in dark-adapted retinae whereby the Delta R(in) (a n increase) became the same for short- and long-wavelengths. The chrom atic Delta R(in), difference could be recovered by light adaptation or application of sodium nitroprusside to the dark-adapted retinae. Conv ersely, the equal-voltage chromatic Delta R(in) difference was elimina ted by injection of N-G-monomethyl-L-arginine into H1HCs of the light- adapted retinae or by treating the retinae with 2-amino-4-phosphonobut yrate (APE). These results suggest that H1HCs of the carp retina posse ss distinct postsynaptic mechanisms which mediate short- and long-wave length signal transmission. Furthermore, it appears that the short-wav elength-sensitive pathway is active only during the light-adapted stat e of the retina. Taken together, therefore, the short-wavelength trans mission to HIHCs probably operates on an APE-sensitive glutamate recep tor, with nitric oxide as a light-adaptive messenger. (C) 1997 Elsevie r Science Ireland Ltd.