Effects of Taurine and Light on Retinal GABA Content and the Efflux of 14C-GABA and 14C-Aspartate from Frog Retina
GABA content of isolated, dark adapted frog retina was found to be 3.15 ± 0.28 mM. After 30 minutes of exposure to intense light (200 1x), retinal GABA levels increased about 70%. Interestingly, incubation of dark adapted retina for 30 minutes with medium containing 0.4 mM taurine also led to a 70% increase in GABA levels. Since the light-induced elevation in GABA content was reduced over 50% by a simultaneous injection of 0.02 mM strychinine, it is likely that the light-induced GABA change is partly mediated by the release of taurine from the retina seen after light exposure. However, incubation of isolated retina with medium containing increasing concentrations of taurine (1, 2 and 20 mM), caused a progressive rise in 14C-GABA efflux from retina that was preloaded with 2.2 μM GABA and exposed to dim light (0.05 1x). It was also shown that taurine (1 and 5 mM) dramatically reduced 14C-aspartate efflux from retina preloaded with radioactive aspartate and exposed to dim light conditions. By comparison, intense light stimulation (40 1x) reduced basal 14C-aspartate efflux while dark exposure increased 14C-aspartate loss from the isolated retina. We found that taurine depressed the b-wave signal of frog retina, with the maximum effect occurring at a concentration of 1 mM. Addition of strychnine (0.4 mM) reversed the taurine effect on the b-wave, indicating that taurine receptors must be present in the inner retina. By contrast, taurine (0.1 – 20 mM) had no effect on the P111 component of the ERG initiated by either aspartate or cobalt. However, taurine exerted a modest depressant activity on P111 initiated by glutamate. The significance of these data relative to the putative neurotransmitter function of taurine in the inner retina is discussed.
KeywordsBackground Illumination Gaba Content Frog Retina Neuroactive Amino Acid Gaba Efflux
Unable to display preview. Download preview PDF.
- 4.Haroutounian, J.E., Gevorgian, G.A., and Petrosssian, A.M., 1981, The effect of illumination level on 14C-GABA efflux from isolated frog retina, J. Evolutional Biochem. and Physiol.(Russ.), 17:542–546.Google Scholar
- 5.Haroutounian, J.E. and Petrossian, A.M., 1982, The action of illumination level on the efflux of 3H-taurine from the isolated frog retina, Armenian Biol. J (Russ), 35:259–264.Google Scholar
- 7.Lake, N. and Orlowski, J., 1995, Cellular studies of the taurine transporter. Abstracts of International Taurine Symposiu. 1995, Taurine: Basic and Clinical Aspects, Osaka, Japan, pp. 43.Google Scholar
- 9.Lima, L., Drujan, B., and Matus, P., 1990, Spatial distribution of taurine in the teleost retina and its role in retinal tissue regeneration, in: Prog. Clin. Biol. Res. “Taurine: Functional Neurochemistry, Physiology and Cardiology”, Pasantes-Morales, H., Martin, D.L., Shain, W., and Martin del Rio, R., eds., Wiley-Liss, Inc. New York, Vol. 351, pp. 103–112.Google Scholar
- 18.Udenfriend, S., 1962, in: Fluorscence assay in biology and medicine, pp. 185, Acad. Press, NY.Google Scholar