Substance P induces ion secretion in mouse small intestine through effects on enteric nerves and mast cells

We used genetically mast cell-deficient WBB6F₁ W/W(v) (W/W(v)) mice and congenic WBB6F₁ +/+ normal (+/+) mice to examine the role of mast cells in substance P-induced intestinal ion secretion. Isolated sheets prepared from segments of the midportion of the small intestine were studied in Ussing chambers. Substance P caused a dose-dependent increase in short-circuit current (I(sc)) that was ~50% less in intestine from W/W(v) than from +/+ mice. Similar results were obtained for substance P-(4-11) (the COOH terminus) and substance P methyl ester [a selective neurokinin (NK)-1 agonist]. Histamine H₁ or H₂ antagonists reduced the I(sc) responses to substance P in intestine from +/+ mice but had no effect in intestine from W/W(v) mice. In addition, reconstitution of intestinal mast cells in W/W(v) mice by intravenous injection of +/+ bone marrow cells normalized the tissues' secretory responses to substance P or substance P methyl ester. However, in W/W(v) and +/+ mice, the selective NK₁ antagonist CP-96345 virtually abolished intestinal responses to substance P, and the responses were also markedly inhibited by neural blockade with tetrodotoxin. In contrast, in tetrodotoxin-pretreated intestine, histamine antagonism caused a further reduction in the responses to substance P only in +/+ mouse tissues. Taken together, our results suggest that the effects of substance P on intestinal I(sc) responses are largely due to binding of the COOH terminus to NK₁ receptors but that the neuropeptide acts via effects on enteric nerves and mast cells. The data thus support the concept that mast cells and enteric nerves participate in the regulation of substance P-induced intestinal ion secretion.