Effect of electrical stimulation and high potassium concentrations on the efflux of [¹⁴C] glycine from slices of spinal cord

The effects of electrical stimulation and solutions containing a high concentration of potassium on the efflux of [(14)C] glycine from slices of rat spinal cord have been studied.2. Slices of cord were incubated with [(14)C] glycine which rapidly accumulated in the tissue. The slices were then superfused in a small chamber and the radioactivity released from the tissue was measured. After superfusion for 60 min, 98% of the radioactivity remaining in the tissue was present as unchanged glycine.3. The spontaneous efflux of [(14)C] glycine consisted of an initial rapid phase followed by a much slower release of [(14)C] glycine. After superfusion for 60 min, more than 65% of the radioactivity taken up during the incubation period was retained by the tissue.4. When the slices were depolarized by electrical stimulation or by solutions containing a high concentration of potassium (40 mM), a striking increase in the efflux of [(14)C] glycine was produced. This effect was not reduced by the absence of calcium ions in the superfusion medium.5. Electrical stimulation produced similar increases in the efflux of [(3)H] GABA and [(14)C] glutamate from slices of cord but had no significant effects on the efflux of [(3)H] alanine or [(14)C] urea.6. The results are consistent with the suggestion that glycine may be an inhibitory synaptic transmitter substance in the mammalian spinal cord.