THE SUBCELLULAR LOCALIZATION OF Ach SYNTHESIS IN RAT STRIATAL SYNAPTOSOMES INVESTIGATED WITH THE USE OF TRITON X-100

—The regulation of ¹⁴C]ACh synthesis was studied in rat striatal synaptosomes incubated in presence of various concentrations of Triton X-100, using 2-¹⁴C]pyruvate or 6-¹⁴C]glucose as precursors. The progressive rupture of the cytoplasmic and mitochondrial compartments induced by the non-ionic detergent was followed by studying the release, into the incubating medium, of lactate dehydrogenase and choline acetyltransferase (ChAc) and of fumarate hydratase, respectively. ³H]Choline uptake (1 μm ) was measured to determine the activity of the high affinity choline permease. ¹⁴CO₂ formation from 2-¹⁴C]pyruvate was used as an index of the Krebs cycle activity. The rate of ¹⁴C]ACh synthesis from 2-¹⁴C] pyruvate was dependent on the Triton X-100 concentration; the ester formation decreased between 0·001% (v/v) and 0·010%, but increased again beyond this concentration of detergent. This last phenomenon was interpreted as the result of an extracellular synthesis of ACh involving pyruvate dehydrogenase and ChAc. At 0·002% Triton X-100 the ¹⁴CO₂ formation was not affected, indicating a normal mitochondrial activity. The decrease of ¹⁴C]ACh synthesis observed up to this detergent concentration could be correlated to the decline of the highaffinity choline permease activity. In these experimental conditions, the ester synthesis could not be restored by the addition of large amounts of choline in the incubating medium suggesting that the molecules of choline must cross the high-affinity choline permease system in order to be acetylated. This could indicate a close association between the permease and choline acetyltransferase.