The uptake of [14C]glycine by slices of mammalian spinal cord

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Abstract
1. The accumulation of [(14)C]glycine by slices of mammalian spinal cord has been measured.2. When slices of rat cord were incubated at 37 degrees C in a medium containing [(14)C]glycine, tissue:medium ratios of about 30:1 were attained after a 40 min incubation.3. After incubations at 37 degrees C for 40 min, almost all (98%) the radioactivity in the tissue was present as unchanged [(14)C]glycine.4. The process responsible for [(14)C]glycine uptake showed many of the properties of an active transport system: it was temperature sensitive, required the presence of sodium ions in the external medium, was inhibited by dinitrophenol and ouabain and showed saturation kinetics.5. The estimated K(m) value of glycine was 3.1 x 10(-5)M, and V(max) was 0.48 mu-mole/min.g cord.6. The uptake of [(14)C]glycine was not affected by the presence of large molar excesses of L-histidine, L-proline, L-aspartate, L-glutamate, L-valine or GABA, but was inhibited in the presence of L-alanine and L-leucine.7. The uptake of [(14)C]glycine was not reduced by strychnine, but a significant reduction in uptake was produced by p-hydroxymercuribenzoate.8. The uptake of [(14)C]glycine by the grey matter of rabbit spinal cord was 2 to 6 times greater than the uptake by slices of white matter incubated under the same conditions.9. Rat cerebral cortex, cerebellar cortex and medulla also accumulated [(14)C]glycine, and the uptake by the tissue slices in vitro appeared to parallel the concentration of glycine in these areas in vivo.10. It is suggested that the glycine uptake system may represent a possible mechanism for the inactivation of glycine at inhibitory synapses in the spinal cord.