Assessment of acetylcholine release from myenteric plexus of guinea-pig colon

Due to a complex mechanical tissue response to electrical stimulation, a colonic smooth muscle-myenteric plexus (SMMP) preparation, combined with radiolabelling techniques for assessing the acetylcholine release, has been developed to investigate intrinsic cholinergic nerve activity in the guinea-pig colon. Electrical field stimulation of the preparation gave reproducible release of label which was inhibited by tetrodotoxin. Release increased proportionally with the strength of stimulus (130, 150, 195 and 250 mA), but was inversely proportional to frequency of stimulation for a fixed number of pulses, 1 Hz releasing more than 10 Hz. Electrical stimulation of the tissue during incubation with [3H]choline enhanced the release by subsequent field stimulation. Release of label increased progressively towards the distal end of the colon.