Potassium-stimulated release of radiolabelled taurine and glycine from the isolated rat retina.
The release of preloaded [3H]glycine and [3H]taurine in response to a depolarising stimulus (12.5-50 mM KCl) has been studied in the superfused rat retina. High external potassium concentration immediately increased the spontaneous efflux of [3H]glycine, the effect of 50 mM K+ apparently being abolished by omitting calcium from the superfusing medium. In contrast, although high potassium concentrations increased the spontaneous efflux of [3H]taurine from the superfused rat retina, this release was not evident until the depolarising stimulus was removed from the superfusing medium. The magnitude of this "late" release of [3H]taurine was dependent on external K+ concentrations, and appeared immediately after cessation of the stimulus irrespective of whether it was applied for 4, 8, or 12 min. Potassium (50 mM)-induced release of taurine appeared partially calcium-dependent, being significantly reduced (p less than 0.01) but not abolished by replacing calcium with 1 mM EDTA in the superfusate. High-affinity uptake systems for both [3H]glycine and [3H]taurine were demonstrated in the rat retina in vitro (Km values, 1.67 microM and 2.97 microM; Vmax values, 19.3 and 23.1 nmol/g wet weight tissue/h, respectively). The results are discussed with respect to the possible neurotransmitter roles of both amino acids in the rat retina.
D000818:Animals; D005998:Glycine / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism*; D014316:Tritium
D014316:Tritium; D013654:Taurine; D011188:Potassium; D005998:Glycine