Effects of bradykinin B2 receptor stimulation at submucosal ganglia from rat distal colon

Bradykinin acts as an inflammatory mediator in the gut. In the present study we characterized bradykinin-induced changes in the intracellular calcium concentration ([Ca2+]i) in whole-mount submucosal preparations from rat distal colon and examined the bradykinin receptors and subsequent signalling cascades involved. Bradykinin (2 · 10− 10–2 · 10− 7 mol/l) evoked a concentration-dependent increase in [Ca2+]i in about 90% of the investigated neurones. This Ca2+ response was abolished by the bradykinin B2 receptor antagonist HOE 140. The B2 receptor agonist [Hyp3]-bradykinin mimicked the kinin response. In contrast, the B1 receptor antagonist [des-Arg10]-HOE 140 and the B1 receptor agonist bradykinin fragment 1–8 were ineffective. Immunohistochemical experiments confirmed the presence of bradykinin B2 receptors in submucosal neurones. The effect of bradykinin on [Ca2+]i was not mediated by a release of prostaglandins, as it was resistant against the cyclooxygenase inhibitor indomethacin. Blocking of Gq/11 proteins with YM-254890 suppressed the action of bradykinin, revealing that neuronal bradykinin B2 receptors are coupled to this G protein. However, the subsequent signalling cascade differed from the classical phospholipase C signalling pathway, as the bradykinin response was resistant against the phospholipase C inhibitor U-73221, the ryanodine receptor antagonist dehydroryanodine, and only marginally sensitive against the blocker of IP3-receptors xestospongin C. Vice versa, the effect of bradykinin was nearly completely dependent on the presence of external Ca2+ and could be reduced by lanthanum, a blocker of voltage-operated Ca2+ channels, suggesting that the bradykinin-induced Ca2+ response is achieved by an influx from the extracellular space via voltage-operated Ca2+ channels.