AJP - Gastrointestinal and Liver Physiology, Vol 247, Issue 3 253-G260, Copyright © 1984 by American Physiological Society
Chymotrypsin, ileal chloride transport, and neurotransmitters
K. A. Hubel
Electrical field stimulation (EFS) depolarizes nerves and causes chloride
secretion by mucosa of rabbit ileum mounted in a flux chamber. To test the
hypothesis that the transmitter is a peptide, we determined whether the EFS
response was prevented by the endopeptidase chymotrypsin (CT). Serosal, but
not mucosal, addition of CT (200 micrograms/ml) reduced the short-circuit
current (Isc) response to EFS by 90% or more. CT also reduced Cl absorption
by decreasing the mucosal-to-serosal flux, but it did not affect net Na
absorption. CT prevented the response to vasoactive intestinal
polypeptides, but the response returned when CT activity was eliminated.
The response to EFS did not return, however, implying that CT damaged cells
that released transmitter or epithelial target cells. CT reduced the Isc
response to serotonin by 69% and to A23187 by 10% and did not affect the
theophylline response. We conclude that 1) the effects of CT on cell
function limit its usefulness in identifying peptide neurotransmitters in
epithelium, 2) CT irreversibly inhibits ion transport responses to EFS and
to serotonin, and 3) CT reduces absorption of Cl probably by affecting a
calcium pathway that modifies Cl transport.
