STIMULATION OF PHOSPHATIDYLINOSITOL HYDROLYSIS, PROTEIN-KINASE-C TRANSLOCATION, AND MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVITY BY BRADYKINININ RAT VENTRICULAR MYOCYTES - DISSOCIATION FROM THE HYPERTROPHIC RESPONSE

In ventricular myocytes cultured from neonatal rat hearts, bradykinin (BK), kallidin or BK(1-8) [(Des-Arg(9))BK] stimulated PtdInsP(2) hydro lysis by 3-4-fold. EC(50) values were 6 nM (BK), 2 nM (kallidin), and 14 mu M [BK(1-8)]. BK or kallidin stimulated he rapid (less than 30 s) translocation of more than 80% of the novel protein kinase C (PKC) is oforms nPKC-degrees and nPKC-epsilon from the soluble to the particula te fraction. EC(50) values for nPKC-delta translocation by BK or kalli din were 10 and 2 nM respectively. EC(50) values for nPKC-epsilon tran slocation by BK or kallidin were 2 and 0.6 nM respectively. EC(50) val ues for the translocation of nPKC-delta and nPKC-epsilon by BK(1-8) we re more than 5 mu M. The classical PKC, cPKC-alpha, and the atypical P KC, aPKC-zeta, did not translocate. BK caused activation and phosphory lation of p42-mitogen-activated protein kinase (MAPK) (maximal at 3-5 min, 30-35% of p42-MAPK phosphorylated). p44-MAPK was similarly activa ted. EC(50) values for p42/p44-MAPK activation by BK were less than 1 nM whereas values for BK(1-8) were more than 10 mu M. The order of pot ency [BK approximate to much greater than kallidin BK(1-8)] for the st imulation of PtdInsP(2) hydrolysis, nPKC-delta and nPKC-epsilon transl ocation, and p42/p44MAPK activities suggests involvement of the B-2 BK receptor subtype. In addition, stimulation of all three processes by BK was inhibited by the B-2 BK receptor-selective antagonist HOE140 bu t not by the B-1-selective antagonist Leu(8)BK(1-8). Exposure of cells to phorbol 12-myristate 13-acetate for 24 h inhibited subsequent acti vation of p42/p44-MAPK by BK suggesting participation of nPKC (and pos sibly cPKC) isoforms in the activation process. Thus, like hypertrophi c agents such as endothelin-1 (ET-1) and phenylephrine (PE), BK activa tes PtdInsP(2) hydrolysis, translocates nPKC-delta and nPKC-epsilon, a nd activates p42/p44-MAPK. However, in comparison with ET-1 and PE, BK was only weakly hypertrophic as assessed by cell morphology and patte rns of gene expression. This difference could not be attributed to dis similarities between the duration of activation of p42/p44-MAPK by BK or ET-1. Thus activation of these signalling pathways alone may be ins ufficient to induce a powerful hypertrophic response.