Influence of enteric cholinergic neurons on mucosal transport in guinea pig ileum

Abstract

Electrical field stimulation was used to activate enteric neurons in the guinea pig ileum in order to determine the involvement of intramural cholinergic motor neurons in the control of mucosal Na and Cl transport. Rectangular, bipolar stimulus pulses evoked a tetrodotoxin[TTX]-sensitive biphasic increase in short-circuit current (Isc) that was due to an increase in active Cl secretion without any effect on active Na absorption. During activation of enteric neurons, atropine, in concentrations .gtoreq. 5 .times. 10-8 M, reversibly abolished the rapid phase of the Isc and reduced the maximum sustained response to 40-50% of control values. Atropine reduced Cl secretion evoked by electrical stimulation and had no effect on sodium fluxes. Basal rates of Na and Cl transport and tissue conductances were not altered by atropine. When muscarinic receptors were maximally stimulated with 10-5 M carbachol, activation of enteric nerves increased Isc to 46% of control values. Bethanechol and eserine increased base-line Isc, and this effect was blocked by atropine but not by TTX. The increase in Isc evoked by bethanechol was due to an increase in active Cl secretion. Acetylcholine released by activation of enteric cholinergic motor neurons evidently acts at muscarinic receptors on enterocytes to stimulate Cl secretion.