Acetylcholine release from colonic submucous neurons associated with chloride secretion in the guinea pig

Electrical field stimulation of submucous neurons in the guinea pig distal colon evokes an increase in chloride secretion sensitive to cholinergic blockade. This study was undertaken in the guinea pig to determine the feasibility of measuring acetylcholine (ACh) release simultaneously with ion transport in sheets of colonic submucosa/mucosa set up in flux chambers modified for perfusion of the submucosal surface. Release of [3H]ACh was determined in the absence of cholinesterase inhibitors as the stimulus-evoked outflow of 3H from preparations preloaded with [3H]choline. [3H]ACh released in response to electrical stimulation correlated with short-circuit current at frequencies from 0.5 to 10 Hz. At 5 and 10 Hz, the stimulus-evoked release of [3H]ACh decreased during subsequent stimulation periods. The stimulus-evoked increase in [3H]ACh was attenuated by tetrodotoxin. [3H]ACh release evoked at stimulus frequencies of 0.5-10 Hz was not altered by atropine despite a reduction in short-circuit current. This study illustrates the feasibility of measuring ACh release simultaneously with ion transport in flux chambers. The results provide new information on the response characteristics of colonic submucous neurons and provide direct evidence for regulation of chloride secretion by ACh.