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S. Bulley, W. Shen; Neuromodulatory Role of Taurine in Glutamate Transmission in Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5790.
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© ARVO (1962-2015); The Authors (2016-present)
Taurine is known to be critical for many functions in the CNS including neurodevelopment, calcium modulation, osmoregulation and neuroprotection. It is highly abundant in the retina however its role in the network is poorly understood. The aim of this study is to determine the regulation of excitatory transmission by taurine in the retina.
To study the effect of taurine, recordings were made on isolated third-order neurons (amacrine and ganglion cells), from larval tiger salamanders (Ambystoma tigrinum), using the whole-cell voltage clamp method. All the chemicals were locally puffed on the neurons using a DAD-VM system (ALA Scientific Co.). The data were recorded with an EPC-10 amplifier and processed with HEKA Patchmaster and Igor Pro software.
Immunocytochemical study showed that taurine was present in high concentrations in the photoreceptors and OFF-bipolar cells. In the third-order neurons, postsynaptic neurons of the OFF-bipolar cells, 10µM taurine has a biphasic effect on glutamate current. In those cells with a weak glutamate current response (less than 25pA) taurine enhances the current. Taurine suppresses the response in those neurons with a strong glutamate response (greater than 25pA). This low dose of taurine produced no current and had no effect on glutamate reversal potential. Suppression of glutamate response was reversed by strychnine, bicuculline and picrotoxin, however enhancement of weak glutamate current was not inhibited by strychnine. A significant reduction in kainate and AMPA current (co-applied with cyclothiazide) by taurine was also observed in the neurons, suggesting that the regulation is mainly present in non-NMDA subtype receptors. The effects of inhibitory neurotransmitters glycine (5µM) and GABA (1µM) on glutamate current did not repeat the effect of taurine in the same cell, suggesting that different mechanisms are involved.
Taurine is possibly released from OFF-bipolar cells with glutamate that activates kainate and AMPA sensitive receptors in the third-order neurons. Taurine at a physiological concentration plays a neuromodulatory role that increases weak glutamate transmission and suppresses strong glutamate transmission. This effect of taurine might improve the dynamic range for excitatory signaling in the inner retinas.
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