Differential Effects of Light and Dark Adaptations on Function and Metabolism of Retinal Taurine and γ-Aminobutyric Acid (GABA)
It has been well established that taurine (2-aminoethanesulfonic acid) is present at a high level in the vertebrate retina, especially in photoreceptor cells (9). In addition, evidence suggesting possible roles of taurine as a neuromodulator or neurotransmitter in the retina, such as the presence of Na+-dependent high affinity uptake of taurine (10), release of taurine by light stimulation (20), and suppressive effect of exogenously applied taurine on the b wave of the electroretinogram (ERG) (1), has been reported. On the other hand, it has been found that the highest levels of γ-aminobutyric acid (GABA) and 1-glutamate decarboxylase (GAD) activity are present in the inner plexiform layer of frog retina (7). Moreover, various pieces of evidence indicating GABA may act as an inhibitory neurotransmitter in vertebrate retina, such as specific Na+- and energy-dependent high affinity uptake (5), inhibition of the b wave of the ERG (22), and binding of (3H)-muscimol (a GABA agonist) to GABA receptor (21) have been presented.
KeywordsDark Adaptation Gaba Content Vertebrate Retina Taurine Content High Affinity Uptake
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