RELEASE OF [³H]GABA FROM IN VITRO PREPARATIONS: COMPARISON OF THE EFFECT OF DABA AND β‐ALANINE ON THE K⁺ AND PROTOVERATRINE STIMULATED RELEASE OF [³H]GABA FROM BRAIN SLICES AND SYNAPTOSOMES¹

Abstract

Abstract It has been proposed that the major portion of [ 3 H]GABA released from rat cortical slices upon exposure to high K + comes from a neuronal pool. Using carrier mediated exchange diffusion of DABA or β ‐alanine in the superfusion medium for GABA in the slice as a technique for manipulating neuronal and glial pools of GABA, it was found that DABA but not β ‐alanine substantially reduced the K + stimulated release of [ 3 H]GABA. The present study using synaptosomes as an in vitro model of the nerve ending was undertaken to ascertain whether this neuronal pool of releasable [ 3 H]GABA was associated with a specific transmitter pool in nerve endings. A continuous superfusion system employing a Ca 2+ pulse to produce a calcium coupled release (L evy et al , 1973) was used to study the effect of two concentrations (20 μ m , 1 m m ) of DABA and β ‐alanine on the release of [ 3 H]GABA from synaptosomes. In contrast to the results in slices, DABA at both concentrations had no effect on the release of [ 3 H]GABA from synaptosomes in spite of evidence that exchange diffusion was occurring. With protoveratrine as the releasing agent there was no effect of DABA on the release of [ 3 H]GABA from either slices or synaptosomes. The results suggest that the major portion of [ 3 H]GABA released from cortical slices by high K + comes from a non‐transmitter pool in the neuron. Use of K + stimulated release of amino acids from cortical slices as a criterion for neurotransmitter function must be viewed with caution.