Threshold requirements for oxygen in the release of acetylcholine from, and in the maintenance of the energy state in, rat brain synaptosomes.

An oxystat was designed to enable maintenance of very low, predetermined oxygen tensions (below 1 microM) in incubated suspensions of synaptosomes. The oxygen thresholds for the energy state (ATP and creatine phosphate levels), for lactate production, and for acetylcholine release were compared. The approximate thresholds (microM O2) in veratridine-stimulated preparations were: oxygen consumption, 10; ATP, 10; creatine phosphate, 15; lactate release, 20; and acetylcholine release, 25. The results for release of total acetylcholine and of the acetylcholine newly synthesized from [14C]glucose were indistinguishable. The results from this study are discussed in relation to hypoxia and to reported in vivo observations.