Ion transport in human cecum, transverse colon, and sigmoid colon in vitro. Baseline and response to electrical stimulation of intrinsic nerves.

In a flux chamber study of ion transport in human colon, we compared baseline rates with those measured during electrical stimulation of intrinsic nerves. In baseline studies, sodium was absorbed throughout, but maximally in transverse colon. In cecum, sodium absorption accounted for the short circuit current and chloride was not absorbed. Chloride was absorbed in transverse and sigmoid colon, however. Residual current was minimal in cecum and transverse colon, but increased in sigmoid colon. Neural stimulation caused chloride secretion in cecum, reduced chloride absorption in sigmoid colon, but caused no change in transverse colon; sodium absorption decreased in cecum. A neurotransmitter of unknown identity affects baseline short circuit current in sigmoid colon. Half of the increase in short circuit caused by neural stimulation in sigmoid colon is mediated by muscarinic receptors. The identity of the other transmitter(s) is not known. It is not substance P or histamine. The three divisions of the colon differ in relative rates of baseline ion transport and in their transport responses to intrinsic nerve stimulation.