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New insights into the neuromodulatory role and potential action site of taurine in retinal neurons
Title
New insights into the neuromodulatory role and potential action site of taurine in retinal neurons.
Creator
Bulley, Simon, Charles E. Schmidt College of Science, Department of Biomedical Science
Abstract/Description
Taurine is the second most abundant amino acid in the CNS after glutamate and its functions have been found largely related to intracellular calcium ([Ca2+]i) modulation, osmoregulation, membrane stabilization, reproduction and immunity. The action of taurine has also been implicated in neurotransmission and neuromodulation though its specific sites of action are not fully understood. Isolated retinal neurons from the larval tiger salamanders (Ambystoma tigrinum) were used as a model to study...
Show moreTaurine is the second most abundant amino acid in the CNS after glutamate and its functions have been found largely related to intracellular calcium ([Ca2+]i) modulation, osmoregulation, membrane stabilization, reproduction and immunity. The action of taurine has also been implicated in neurotransmission and neuromodulation though its specific sites of action are not fully understood. Isolated retinal neurons from the larval tiger salamanders (Ambystoma tigrinum) were used as a model to study the neuromodulatory role of taurine in the CNS and to gain insights into its potential sites of action. A combination of techniques was used, including whole-cell patch clamp recording to study taurine's regulation of voltage-gated potassium (K+) and Ca2+ channels and Fluo-4AM Ca2+-imaging to study taurine's regulation of glutamate-induced [Ca2+] I,. Taurine was shown to suppress of glutamate-induced [Ca2+] l, in a dose dependent manner. This suppression was mostly sensitive to the glycine rece ptor antagonist Strychnine but insensitive to any GABA receptor antagonist. The remaining strychnine-insensitive effect was inhibited with the protein kinase A (PKA) inhibitor, PKI, suggesting that there was an additional metabotropic pathway. Moreover, using the protein kinase C (PKC) inhibitor, GF109203X, there was an enhancement in strychnine-insensitive taurine's regulation. Taurine inhibits voltage-gated Ca2+ channels in the retinal neurons and has a dual effect on voltage-gated K+ channels. Taurine causes an increase in K+ current amplitude which is further enhanced with PKI and blocked with GF109203X, suggesting that it is through a PKC-dependent pathway negatively controlled by PKA-dependent pathway., There is a suppression of K+ current by taurine with intracellular application of GF109203X, suggesting that the reduction is through a PKA-dependent pathway. With both PKC and PKA inhibitors there is no longer an enhancement in maximum amplitude but a shift of volt dependence on a hyperpolarizing direction. Taurine's enhancement of K+ current is blocked by the Kv1.3 subtype antagonist Margatoxin, with Kv1.3 accounting for the majority of delayed-rectifier sustained current in bipolar and amacrine cells, as well as 50% of ganglion cells. Interestingly, the enhancement of K+ current by taurine is blocked by 5HT2A antagonist MDL11939, suggesting that activation of PKC is through this metabotropic serotonin receptor subtype. The suppression of voltage-gated Ca2+ channels is reversed with a combination of MDL11939 and the 5HT1A antagonist NAN-190. These results provide the evidence that the natural effect of taurine in the retinal neurons might be dependent on the activation of both 5HT1A and 5HT2A receptors. The high apparent activity of taurine on 5HT receptors could have important implication for the actions of taurine in central brain in which taurine has been known to be beneficial for improving mental health, as well as learning and memory processes.
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Date Issued
2010
PURL
http://purl.flvc.org/FAU/2953206
Subject Headings
Biological transport, Eye, Physiology, Taurine, Physiological effect, Taurine, Therapeutic use, Central nervous system, Physiology
Format
Document (PDF)