| Abstract: | The spontaneous release of acetylcholine (ACh) from the guinea-pig myenteric plexus - longitudinal muscle preparation superfused at a constant rate in the presence of physostigmine was 10 nmol-g-1-h-1. This release was decreased to one-third by tetradotoxin or by MnCl2 and increased 2.5 times by 0.1 Hz and 20 times by 16 Hz stimulation. The formation of 3H]ACh from 3H]choline increased from 3 to 33 nmol-g(-1)-h(-1) when the concentration of 3H]choline was increased from 1 muM to 50 muM. The rate of 3H]ACh formation was not affected by tetrodotoxin, MnCl2, or physostigmine in the absence of stimulation. It was increased by 50% by 0.1 Hz and by 100% by 16 Hz stimulation during the first 9 min of exposure to 3H]choline but not subsequently. The myenteric plexus - longitudinal muscle preparation contains 200 nmol/g choline. Results suggest that the apparent small 3H]ACh formation from low concentrations of 3H]choline is due to the dilution of 3H]choline by endogenous choline. The major part of 3H]ACh formation appears to be due to the intracellular turnover of ACh while the evoked release of 3H]ACh appears to originate from a small pool. |
