Distension evoked mucosal secretion in human and porcine colon in vitro

It was suggested that intestinal mucosal secretion is enhanced during muscle relaxation and contraction. Mechanisms of mechanically induced secretion have been studied in rodent species. We used voltage clamp Ussing technique to investigate, in human and porcine colonic tissue, secretion evoked by serosal (P_ser) or mucosal (P_muc) pressure application (2–60 mmHg) to induce distension into the mucosal or serosal compartment, respectively. In both species, P_ser or P_muc caused secretion due to Cl^- and, in human colon, also HCO₃^- fluxes. In the human colon, responses were larger in proximal than distal regions. In porcine colon, P_muc evoked larger responses than P_ser whereas the opposite was the case in human colon. In both species, piroxicam revealed a strong prostaglandin (PG) dependent component. P_ser and P_muc induced secretion was tetrodotoxin (TTX) sensitive in porcine colon. In human colon, a TTX sensitive component was only revealed after piroxicam. However, synaptic blockade by ω-conotoxin GVIA reduced the response to mechanical stimuli. Secretion was induced by tensile rather than compressive forces as preventing distension by a filter inhibited the secretion. In conclusion, in both species, distension induced secretion was predominantly mediated by PGs and a rather small nerve dependent response involving mechanosensitive somata and synapses.