FURTHER EXPERIMENTS ON THE UPTAKE OF ACETYLCHOLINE AND ATROPINE AND THE RELEASE OF ACETYLCHOLINE FROM MOUSE BRAIN CORTEX SLICES AFTER TREATMENT WITH PHOSPHOLIPASES

—Uptake of acetylcholine (ACh) in mouse brain cortex slices, previously shown with ACh synthesized from tritiated choline is confirmed with acetyl1-¹⁴C]choline. Radioactivity from tritiated sodium acetate also accumulates in slices, but forms hardly any ACh. Uptake of ACh increases in a Ca²⁺-free medium, decreases again upon addition of a 3 × 10⁵ molar concentration of an anticholinergic benzilate compound and is completely blocked by the same compound at 3 × 10³ m. Slices preloaded with labelled ACh release, after extensive washing, some of their radioactivity into an outer medium free from ACh. Phospholipase, A or C, increases the release of radioactivity from the slices. An equilibrium is reached both with controls and phospholipase-treated slices. Remaining radioactivity seems to be due to bound ACh. Calcium and magnesium ions have no effect on the uptake of tritiated atropine, although low concentrations of Ca²⁺ decrease the effects of phospholipase C on atropine uptake. The inhibitory effect of K⁺ on atropine uptake disappears completely after treatment with small amounts of phospholipase A, but even high concentrations of phospholipase C have no effect.