Release of (3H)GABA and (14C)glutamic acid from rat cortex slices: the relationship between the tissue pool size and rates of spontaneous and electrically induced release.
A constant fraction of the existing tissue pool of (3H)GABA or (14C)glutamic acid was released during electrical stimulation of rat cortex slices. The sum of the amounts of labeled amino acids released spontaneously and by electrical stimulation was constant when stimulated slices were superfused with normal medium or media containing ouabain or a high K+ concentration. The fraction of the total amount released that was attributable to electrical stimulation varied inversely with the amount released spontaneously. Pentobarbital inhibited the accelerated spontaneous release produced by ouabain or high K+ and restored the ability of the slice to respond to electrical stimulation. Electrically induced release was felt to be limited by a theoretical maximum transport velocity of efflux of approximately 5.5% per min.