Bradykinin-induced depolarisation and Ca(2+) influx through voltage-gated Ca(2+) channels in rat submucosal neurons

The aim of the present study was the investigation of the mechanism, by which bradykinin B(2) receptor stimulation evokes an increase of the cytosolic Ca(2+) concentration in rat submucosal plexus. In ganglionic cells within the intact submucosal plexus, the Ca(2+)-response evoked by bradykinin was suppressed by Ni(2+), suggesting that Ca(2+) enters the cell through voltage-gated Ca(2+) channels (Ca(v) channels). Inhibition of Ca(v) channel subtypes P, T and R with omega-agatoxin IVA, flunarizine, and SNX-482 did not affect the response to bradykinin. In contrast, verapamil, omega-conotoxin GVIA, and omega-conotoxin MVIIC attenuated the actions of bradykinin, indicating the involvement of the L-, N- and Q-subtypes of Ca(v) channels. The combination of these three blockers had a strong inhibitory action on the bradykinin response. In order to study the mechanism of activation of Ca(v) channels by bradykinin, isolated submucosal neurons in culture were used. Immunocytochemical stainings revealed that these neurons expressed the bradykinin B(2) receptor, while the B(1) receptor was absent. Isolated submucosal glial cells did not express the bradykinin B(2) receptor. Whole-cell patch-clamp measurements of submucosal neurons showed that bradykinin induced a depolarisation of the membrane in average of 14mV. The ionic mechanism underlying the depolarisation was identified with current measurements at two different membrane potentials (-81 and 0mV). The current associated to Na(+) influx was not changed by bradykinin, whereas the current representing K(+) outflux was reduced by 26%. The present results suggest that at submucosal neurons from the rat colon bradykinin induces a depolarisation by decreasing the K(+) conductance, followed by activation of the Ca(v) channels, which mediates the increase of the cytosolic Ca(2+) concentration.