[Show abstract][Hide abstract] ABSTRACT: Increasing evidence suggests that protein kinase C (PKC) is involved in the Ca(2+) sensitization of various smooth muscle contractions. However, the exact role of PKC on bronchial smooth muscle (BSM) contraction is still unclear. In the present study, to determine the role of PKC activation in the BSM contraction, the effects of phorbol 12,13-dibutyrate (PDBu) on BSM tone were examined in the absence and presence of contractile stimulation. Although PDBu had no effect on the basal tone, the contraction induced by acetylcholine, high K(+) depolarization or Ca(2+) ionophore A23187 was significantly augmented by PDBu. Western blot analyses also revealed that the increase in the level of phosphorylated myosin light chain (MLC) induced by high K(+) depolarization was significantly augmented by PDBu treatment. Interestingly, neither high K(+) depolarization alone nor PDBu alone caused CPI-17 phosphorylation, but a significant phosphorylation of CPI-17 was observed when BSMs were co-stimulated by high K(+) and PDBu. Thus, a certain level of intracellular Ca(2+) might be needed both for an activation of CPI-17 and an induction of contraction induced by PDBu in mouse BSMs.
[Show abstract][Hide abstract] ABSTRACT: To explore the role of protein kinase C (PKC) in the augmented bronchial smooth muscle (BSM) contraction observed in the antigen-induced airway hyperresponsive (AHR) mice, the effects of a PKC activator, phorbol 12,13-dibutylate (PDBu), on BSM contraction were compared between the AHR and control mice. Actively sensitized mice were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge the isometrical contractions of the BSMs were measured. The BSM contraction induced by acetylcholine, but not high K(+) depolarization, was significantly augmented in the AHR mice. In BSMs of control mice, PDBu caused a significant increase in tension when the tissues were precontracted with high K(+), although PDBu itself had no effect on basal tone. The PDBu-mediated contraction was markedly augmented in BSMs of the AHR mice. These findings suggest that an increase in the PKC-mediated signaling is involved in the augmented contraction of BSMs in the antigen-induced AHR mice.
[Show abstract][Hide abstract] ABSTRACT: In airway smooth muscle, protein kinase C (PKC) has been implicated in a number of functional responses including the regulation of contractility. However, the exact role of PKC on bronchial smooth muscle (BSM) contraction is still unclear. In the present study, to determine the role of PKC activation in the BSM contraction, the effects of phorbol 12,13-dibutyrate (PDBu, a direct PKC activator) on BSM tone were examined in the absence and presence of K(+)-induced depolarization stimulation. The force development was not evoked by treatment with 1 µM PDBu alone. However, a strong contraction was induced by PDBu during high K(+) contraction. The contraction induced by PDBu during high K(+) stimulation was significantly abolished by pretreatment with nicardipine, an L-type voltage dependent Ca(2+) channel blocker. In RT-PCR analysis, mRNAs of PKCα, β, γ, δ, ε, η and θ isoforms were detected in mouse BSM. Gö6976 (an inhibitor of PKCs α and β) and rottlerin (an inhibitor of PKCδ) significantly but partially inhibited the PDBu-induced BSM contraction during K(+) stimulation. GF109203X (an inhibitor of PKCs α, β, γ, and ε) completely inhibited the PDBu-induced contraction during K(+) stimulation. In conclusion, it is suggested that the PDBu-induced BSM contraction is dependent on an increase in cytosolic Ca(2+). Furthermore, it is possible that both cPKC and nPKC(s) participate in the PDBu-induced contraction of mouse BSM during K(+) stimulation.