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

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Abstract
1 The effects of electrical stimulation and solutions containing a high concentration of potassium on the efflux of [14C] glycine from slices of rat spinal cord have been studied. 2 Slices of cord were incubated with [14C] 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 [14C] glycine consisted of an initial rapid phase followed by a much slower release of [14C] 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 [14C] 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 [3H] GABA and [14C] glutamate from slices of cord but had no significant effects on the efflux of [3H] alanine or [14C] urea. 6 The results are consistent with the suggestion that glycine may be an inhibitory synaptic transmitter substance in the mammalian spinal cord.