Effects of acetylcholine on phosphate turnover in phospholipides of brain cortex in vitro

Abstract

1. 1. The incorporation of 32P into the ether soluble phospholipides of guinea pig brain cortex slices is increased up to three-fold in the presence of acetylcholine (with eserine). The chloroform soluble phospholipides and the glycerophosphatides show a lesser stimulation. The phospholipide content is not appreciably changed during incubation in the presence or absence of acetylcholine. 2. 2. The minimum effective external concentration of acetylcholine lies between 10 −6 and 10 −5 M. With 2 to 3 hours incubation the specific activities of the brain phospholipides increase linearly with the logarithm of the external acetylcholine concentration over the range tested (10 −5 M to 10 −2 M). 3. 3. The increased incorporation of 32P into the glycerophosphatides is due to an increased turnover of phosphate in preformed phospholipides rather than to an increased synthesis de novo of phospholipides. 4. 4. The stimulation of phosphate turnover in glycerophosphatides in the presence of 10 −2 M acetylcholine is approximately the same in the nuclear, mitochondrial, microsomal and supernatant fractions. 5. 5. Atropine, in very low concentrations (10 −6 M), abolishes the stimulatory effect of acetylcholine (10 −4 M) on phosphate turnover in phospholipides, reducing the turnover about 15% below the level found without acetylcholine or eserine. In higher concentrations (10 −4 to 10 −2 M) atropine stimulates the incorporation of 32P into the phospholipides. 6. 6. The possible significance of the increased phosphate turnover in phospholipides in response to acetylcholine is discussed.