Sodium ion movements and the spontaneous and electrically stimulated release of [³H]GABA and [¹⁴C]glutamic acid from rat cortical slices

The effect on spontaneous and electrically stimulated release of [³H]GABA and [¹⁴C]glutamic acid from rat cortical slices of agents and ionic conditions that affect sodium ion movements, was studied in an in vitro superfusion system. Those conditions that elevated non-inulin Na⁺ content of the slice accelerated spontaneous efflux and inhibited electrically stimulated release of the labeled amino acids. Agents which blocked the entry of Na⁺ with electrical field stimulation failed to diminish release of the amino acids. Therefore, the entry of Na⁺ into the slice with membrane depolarization is not a requirement for amino acid neurotransmitter release from cortical slices in response to electrical field stimulation. The acceleration of spontaneous efflux and inhibition of electrically stimulated release in the presence of an elevated non-inulin Na⁺ content was discussed in relation to sodium coupled transport of amino acids.