Bradykinin modulates pacemaker currents through bradykinin B2 receptors in cultured interstitial cells of Cajal from the murine small intestine

We studied the modulation of pacemaker activities by bradykinin in cultured interstitial cells of Cajal (ICC) from murine small intestine with the whole-cell patch-clamp technique. Externally applied bradykinin produced membrane depolarization in the current-clamp mode and increased tonic inward pacemaker currents in the voltage-clamp mode. Pretreatment with bradykinin B1 antagonist did not block the bradykinin-induced effects on pacemaker currents. However, pretreatment with bradykinin B2 antagonist selectively blocked the bradykinin-induced effects. Also, only externally applied selective bradykinin B2 receptor agonist produced tonic inward pacemaker currents and ICC revealed a colocalization of the bradykinin B2 receptor and c-kit immunoreactivities, but bradykinin B1 receptors did not localize in ICC. External Na ⁺-free solution abolished the generation of pacemaker currents and inhibited the bradykinin-induced tonic inward current. However, a Cl ^- channel blocker (DIDS) did not block the bradykinin-induced tonic inward current. The pretreatment with Ca ²⁺-free solution and thapsigargin, a Ca ²⁺-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the bradykinin-induced action. Chelerythrine and calphostin C, protein kinase C inhibitors or naproxen, an inhibitor of cyclooxygenase, did not block the bradykinin-induced effects on pacemaker currents. These results suggest that bradykinin modulates the pacemaker activities through bradykinin B2 receptor activation in ICC by external Ca ²⁺ influx and internal Ca ²⁺ release via protein kinase C- or cyclooxygenase-independent mechanism. Therefore, the ICC are targets for bradykinin and their interaction can affect intestinal motility.