Bradykinin regulates human colonic ion transport in vitro

Background and purpose: Kinins are acknowledged as important regulators of intestinal function during inflammation; however, their effects on human intestinal ion transport have not been reported. Here, we used muscle‐stripped human colonic tissue and cultured T 84 ‐cell monolayers to study bradykinin (BK) actions on human intestinal ion transport. Experimental approach: Ion transport was measured as changes in short‐circuit current ( I sc ) across colonic epithelia mounted in Ussing chambers. Key results: In intact tissue, there was a distinct polarity to BK‐elicited I sc responses. Whereas basolateral BK stimulated sustained responses (EC 50 =0.5±0.1 μ M ), those to apical BK were more rapid and transient (EC 50 =4.1±1.2 n M ). In T 84 cells, responses to both apical and basolateral BK were similar to those seen upon apical addition to intact tissues. Cross‐desensitization between apical and basolateral domains was not observed. BK‐induced responses were largely due to Cl − secretion as shown by their sensitivity to bumetanide and removal of Cl − from the bathing solution. Studies using selective agonists and antagonists indicate responses to BK are mediated by B 2 receptors. Finally, responses to basolateral BK in intact tissues were inhibited by tetrodotoxin (1 μ M ), atropine (1 μ M ), capsaicin (100 μ M ) and piroxicam (10 μ M ). BK‐stimulated prostaglandin (PG)E 2 release from colonic tissue. Conclusions: BK stimulates human colonic Cl − secretion by activation of apical and basolateral B 2 receptors. Responses to apical BK reflect a direct action on epithelial cells, whereas those to basolateral BK are amplified by stimulation of enteric nerves and PG synthesis. British Journal of Pharmacology (2008) 155 , 558–566; doi: 10.1038/bjp.2008.288 ; published online 7 July 2008