Glycine release

Kerchner, G. A., Wang, G. D., Qiu, C. S., Huettner, J. E., and Zhuo, M. (2001) Direct presynaptic regulation of GABA/glycine release by kainate receptors in the dorsal horn an ionotropic mechanism. Neuron 32,477—488. 

Presynaptic glycine receptors were found to operate at several synapses (Table 1). In the spinal cord, for instance, presynaptic glycine autoreceptors mediated a facilitation of spontaneous glycine release in a tetrodotoxin- and Cd2+-sensitive manner, which is indicative of presynaptic depolarization. An enhancing effect was also observed with action potential-evoked glycine release (Jeong et al. 2003). 

Evidence for the regulation of the release of inhibitory transmitters via presynaptic P2X receptors has also been obtained. In the spinal cord, P2X2 receptor activation facilitated spontaneous glycine release in a tetrodotoxin- and Cd2+-insensitive, but Ca2+-dependent, manner (Rhee et al. 2000). 

Figure 9.4 Hydrolysis of hippuric acid and estimation of the glycine released by ninhydrin. Ninhydrin reacts quantitatively with amino acids to give a purple colour which can be measured spectrophotometrically...

Several authors concluded that the high-affinity uptake system might represent a homoexchange process (Levi and Raiteri, 1974 Simon et al., 1974 Raiteri et al., 1975 Levi et al., 1976). Synaptosome preparations preloaded with [ H]-GABA or [ H]-glycine released them in a dose-dependent manner when... 

To exclude any possible toxicity of the rHC component in our DDV construct, we compared the inhibition of 80 mM stimulated [ H]glycine release due to increasing concentrations of rHC or native BoNT/A holotoxin by the assay described in Methods. In these experiments, the results obtained using the particular batch of toxin showed that BoNT/A was quite toxic, as expected, with an IC50 (toxin concentration to cause 50% inhibition of neuroexocytosis in untreated control cells) of approximately <1 pM and a total inhibition at -O.l nM. 

However, a much higher concentration of rHC, up to 200 nM, did not show any inhibition of PH]glycine release under the same assay conditions (Fig. 2). 

Figure 2. rHC was a safe DDV component to delivery antidotes. Primary cultures of mouse spinal cord were exposed to BoNT/A ( ) or rHC (o) respectively in indicated concentrations for 16 hrs. Potassium-evoked glycine release was measured. Results expressed as percentage glycine release compared with untreated control. Data points are the mean ( SD) of three separate experiments each determined in triplicate. 

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