Modulation of choline transport and acetylcholine synthesis in synaptosomes from different brain regions

Uptake and biotransformation of radioactive choline (3H-Ch) have been studied in P2 fractions from different brain regions of mice treated with different doses of sodium pentobarbital (45-120 mg/kg intraperitoneally) or saline. Sodium dependent uptake (SDU) has been measured as the difference between results of incubations with Na+ in the incubation medium and when the sodium salts were replaced by Trisphosphate and sucrose. The uptake of radioactivity increased during the incubation with 3H-Ch but the proportion of 3H-ACh was the same at all time points. The proportion of 3H-ACh to 3H-Ch in the P2 pellet was 86, 81 and 69 per cent in hippocampus, striatum and cortex, respectively. Omission of sodium ions in the incubation medium reduced uptake of 3H-Ch by about 90 per cent at 1 microM Ch in the incubation medium and the proportion of 3H-ACh to 3H-Ch was only 10 to 20 per cent while the proportion of 3H-PhCh increased from insignificant amounts to between 20 to 30 per cent. There were quantitative regional differences in SDU, a two times greater uptake was obtained in the striatum compared with cortex and hippocampus. Apparent Km and Vmax were 0.9 X 10(-6)M and 71 pmol/mg, respectively, for the cortex of untreated animals. The contribution of endogenous Ch from the P2 fraction to the incubation medium gave a final concentration of 0.5 microM Ch in the standard uptake experiments. The 3H-Ch uptake was significantly reduced in P2 fraction from cortex and hippocampus prepared from mice anaesthetized with sodium pentobarbital while the uptake in P2 fractions from the striatum was unaffected. Sodium pentobarbital treatment did not affect the proportion of 3H-ACh in the pellets.