Bradykinin induced contraction of human gallbladder muscle in vitro

Abstract

Aim To examine the mechanisms of Bradykinin (BK)-induced contraction on human gallbladder muscle and to investigate possible receptors that may mediate this action. Methods A full-thickness segment from the anterior aspect of healthy and stone-hearing gallbladders was removed and placed in cold Krebs solution in an organ bath. Concentration-response curves (CRCs) were obtained for BK (0.1-100/LM). The BK response curves were repeated in the presence of a number of antagonists and channel blockers BI & B2 receptor antagonists, SR 27897 (0.5nM,a CCK-A receptor antagonist), mepyramine (l/LM, a histamine receptor antagonist), atropine (l/LM, a muscarinic receptor antagonist), prazosin (O.l/LM,a adrenoceptor blocker), tetrodotoxin (O.03/LM, a Na channel blocker), quinidine (l/LM, a K channel blocker) and indomethacin (3/LM, a cyclo-oxygenase inhibitor). Extracellular Ca involvement was examined by use of Ca free medium. Ryanodine (lO/LM) was used to examine intracellular involvement. Ethics committee approval for tissue sampling was obtained. Statistical significance was performed using t-test, P < .05 or less was considered as indicative of significance. Results Healthy (n=6) and stone-bearing (n=9) gallbladders showed similar and repeatable CRCs to BK (EDso=4.95 & 5.5/LM). The BK response was significantly reduced only in healthy strips by BI receptor blockade (EDso=31.5/LM) and in both tissue types by B2 receptor blockade (EDso=37.2 & 29./LM). Neither antagonist affected the maximum BK response. No significant rightward shift of the response to BK was observed in the presence of mepyramine (n=4), atropine (n=), prazosin (n=6), tetrodotoxin (n=), quinidine (n=7) or SR27897 (n=5). A significant rightward shift of the curve was noted in the presence of indomethacin (n=20,EDso=55/LM). BK-induced contraction was not modified in Ca-free medium (n=7), however the presence of ryanodine caused a significant rightward shift of the BK dose-response curve (n=7,EDso=46/LM. Conclusion Gallbladder strips contract to BK in a dose-dependent manner. A difference in receptor population seems to exist between normal and stone-bearing gallbladders. BK appears to have a direct myogenic effect on the human gallbladder and this may be mediated by a third BK receptor or a BK-independent mechanism. The contraction occurs independently of extracellular Ca but intracellular Ca is vital. In addition, part of this BK-induced contraction is probably mediated by the release of a cyclo-oxygenasc-dcrived product from the arachidonic acid pathway.