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

摘要

In ventricular myocytes cultured from neonatal rat hearts, bradykinin (BK), kallidin or BK(1-8) [(Des-Arg(9))BK] stimulated PtdInsP(2) hydrolysis 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) isoforms nPKC-degrees and nPKC-epsilon from the soluble to the particulate fraction. EC(50) values for nPKC-delta translocation by BK or kallidin were 10 and 2 nM respectively. EC(50) values for nPKC-epsilon translocation by BK or kallidin were 2 and 0.6 nM respectively. EC(50) values for the translocation of nPKC-delta and nPKC-epsilon by BK(1-8) were more than 5 mu M. The classical PKC, cPKC-alpha, and the atypical PKC, aPKC-zeta, did not translocate. BK caused activation and phosphorylation of p42-mitogen-activated protein kinase (MAPK) (maximal at 3-5 min, 30-35% of p42-MAPK phosphorylated). p44-MAPK was similarly activated. 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 potency [BK approximate to much greater than kallidin BK(1-8)] for the stimulation of PtdInsP(2) hydrolysis, nPKC-delta and nPKC-epsilon translocation, 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 but 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 activation of p42/p44-MAPK by BK suggesting participation of nPKC (and possibly cPKC) isoforms in the activation process. Thus, like hypertrophic agents such as endothelin-1 (ET-1) and phenylephrine (PE), BK activates PtdInsP(2) hydrolysis, translocates nPKC-delta and nPKC-epsilon, and activates p42/p44-MAPK. However, in comparison with ET-1 and PE, BK was only weakly hypertrophic as assessed by cell morphology and patterns of gene expression. This difference could not be attributed to dissimilarities between the duration of activation of p42/p44-MAPK by BK or ET-1. Thus activation of these signalling pathways alone may be insufficient to induce a powerful hypertrophic response.