Co-release of acetylcholine, glutamate and taurine from synaptosomes of Torpedo electric organ.

The amino acid content of Torpedo synaptosomes was investigated. It was found that glutamate and taurine were particularly enriched, their concentration exceeding that of acetylcholine by 50-60%. Other amino acids such as alanine, gamma-aminobutyric acid (GABA), glycine, leucine and phenylalanine were also present, but in smaller quantities. The neurotransmitter-releasing agents gramicidin, calcium ionophore A23187, High K+ and Glycera venom all released acetylcholine, as shown previously. However, both glutamate and taurine were found to be released by these agents together with acetylcholine. The efflux of all 3 compounds was found to be largely calcium dependent.