BRADYKININ REGULATES THE HISTAMINE-INDUCED CA2-KINASE-C ACTIVATION INHUMAN GINGIVAL FIBROBLASTS( MOBILIZATION VIA PROTEIN)

We previously demonstrated that histamine and bradykinin evoke an incr ease in intracellular Ca2+ ([Ca2+](i)) in human gingival fibroblasts b y using a fluorescent Ca2+ indicator Fura-2. In this paper, we further demonstrate the regulation of the histamine-induced Ca2+ mobilization by bradykinin. In fibroblasts stimulated with bradykinin (1 mu M), su bsequent stimulation with histamine (100 mu M) failed to mobilize Ca2, whereas bradykinin induced an increase In [Ca2+](i) in the cells pre -stimulated with histamine. The attenuation of the histamine response was dependent on the concentration of bradykinin for the first stimula tion. Histamine also failed to induce the formation of inositol 1,4,5- trisphosphate in fibroblasts pretreated with bradykinin. In fibroblast s pretreated with bradykinin (1 mu M) for 3 min and then washed with f resh medium, the effect of histamine on [Ca2+](i) quickly returned to the control level. The activation of protein kinase C by phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (PMA) elicited a marked decreas e in histamine-induced Ca2+ mobilization. When the protein kinase C ac tivity was inhibited with H7, a protein kinase C inhibitor, or was dow n-regulated by pretreatment with PMA for 20 h, the inhibitory effect o f PMA on the histamine response was relieved. In the fibroblasts pretr eated with H7 or PMA for 20 h, histamine evoked Ca2+ mobilization even after bradykinin stimulation. These results suggest that the histamin e response is regulated by bradykinin receptor activation via the acti vation of protein kinase C in human gingival fibroblasts.