Uptake and stimulus‐evoked release of [3H]‐γ‐aminobutyric acid by myenteric nerves of guinea‐pig intestine

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Abstract
1 Following preloading with [3H]-γ-aminobutyric acid ([3H]-GABA), in the presence of β-alanine to inhibit glial uptake of the label, electrical stimulation caused a frequency-dependent release of tritium as [3H]-GABA from isolated longitudinal-muscle myenteric-plexus preparations of the guinea-pig ileum and colon. 2 The electrically evoked efflux of [3H]-GABA was Ca2+-dependent, virtually abolished by preventing neuronal conduction with tetrodotoxin, and markedly reduced by preloading with [3H]-GABA in the presence of nipecotic acid which is an inhibitor of high affinity GABA-uptake. Veratridine and KCl were less effective than electrical stimulation in evoking [3H]-GABA release. 3 It is concluded that the electrically stimulated efflux of [3H]-GABA originated from GABAergic neurones of the myenteric plexus which had taken up the label. 4 These results provide further evidence to support the suggestion that GABA is a transmitter in the mammalian enteric nervous system.