Epithelial transport in guinea-pig proximal colon: influence of enteric neurones.

1. The effects of electrical field stimulation and aminophylline on sodium and chloride transport in the guinea-pig proximal colon were examined. 2. Under basal conditions, both sodium and chloride were actively absorbed and the net fluxes of these ions accounted for the short-circuit current. 3. Basal short-circuit current was reduced by furosemide, unchanged by amiloride and increased by aminophylline. The aminophylline-evoked increase in short-circuit current resulted from a reduction in net sodium absorption and abolishment of chloride absorption without a significant effect on residual flux. 4. Electrical field stimulation evoked a tetrodotoxin-sensitive increase in short-circuit current and total tissue conductance. The stimulus-evoked response was unaltered by mucosal amiloride, but was reduced by serosal furosemide. Electrical stimulation of submucosal neurones reduced both sodium and chloride absorption without any effect on residual flux. 5. Atropine had no effect on the basal short-circuit current; however, it reduced, but did not abolish, the neurally evoked response. Carbachol evoked a dose-dependent increase in short-circuit current that was reduced by tetrodotoxin. 6. These results suggest that electrical field stimulation activates submucosal neurones that innervate the epithelium. Release of acetylcholine and other neurotransmitters leads to excitation of receptors on epithelial cells, and an increase in short-circuit current that reflects inhibition of sodium and chloride absorption.