Bradykinin inhibits ceramide production and activates phospholipase D in rabbit cortical collecting duct cells

Recent reports suggest that inflammatory cytokines, growth factors, and vas oconstrictor peptides induce sphingomyelinase (SMase) activity. This result s in the hydrolysis of sphingomyelin (SM) into ceramide, which is implicate d in various cellular functions. Although ceramide regulates phospholipase D (PLD) activity, there is controversy about this relationship. Thus we inv estigated whether the effect of bradykinin (BK), a proinflammatory factor a nd vasodilator, was mediated by ceramide signal transduction and by PLD. In rabbit cortical collecting duct (RCCD) cells, BK increased SM levels and d ecreased ceramide levels in a time-dependent manner. Thus SMase activity wa s inhibited by BK. Also, the production of ceramide was regulated in a conc entration-dependent manner. The BK-B-1 antagonist [Lys-des-Arg(9),Leu(8)]BK did not affect ceramide signal transduction but the BK-B-2 antagonist (Hoe -140) blocked the effect of BK on SMase, suggesting that the BK-B2 receptor mediates BK-induced inhibition of ceramide generation. Our results show th at exogenous SMase significantly hydrolyzed endogenous SM to form ceramide and weakly activated PLD. In contrast, BK induced a significant activation of PLD. However, additive effects of BK and ceramide on PLD activity were n ot observed. We concluded that in RCCD cells, the BK-induced second messeng ers ceramide and phosphatidic acid were generated by distinct signal transd uction mechanisms, namely the SMase and PLD pathways.