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

In ventricular myocytes cultured from neonatal rat hearts, bradykinin (BK), kallidin or BK(1–8) [(Des-Arg⁹)BK] stimulated PtdInsP₂ hydrolysis by 3–4-fold. EC₅₀ values were 6 nM (BK), 2 nM (kallidin), and 14 μM [BK(1–8)]. BK or kallidin stimulated the rapid (less than 30 s) translocation of more than 80% of the novel protein kinase C (PKC) isoforms nPKC-Δ and nPKC-ϵ from the soluble to the particulate fraction. EC₅₀ values for nPKC-Δ translocation by BK or kallidin were 10 and 2 nM respectively. EC₅₀ values for nPKC-ϵ translocation by BK or kallidin were 2 and 0.6 nM respectively. EC₅₀ values for the translocation of nPKC-Δ and nPKC-ϵ by BK(1–8) were more than 5 μM. The classical PKC, cPKC-α, and the atypical PKC, aPKC-ζ, 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. EC₅₀ values for p42/p44-MAPK activation by BK were less than 1 nM whereas values for BK(1–8) were more than 10 μM. The order of potency [BK≈kallidin ≫ BK(1–8)] for the stimulation of PtdInsP₂ hydrolysis, nPKC-Δ and nPKC-ϵ translocation, and p42/p44-MAPK activities suggests involvement of the B₂ BK receptor subtype. In addition, stimulation of all three processes by BK was inhibited by the B₂ BK receptor-selective antagonist HOE140 but not by the B₁-selective antagonist Leu⁸BK(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 PtdInsP₂ hydrolysis, translocates nPKC-Δ and nPKC-ϵ, 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.