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

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... force development was not evoked by treatment with 1 M 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 PKC, β, , , ,  and  isoforms were detected in mouse BSM. Gö6976 (an inhibitor of PKCs  and β) and rottlerin (an inhibitor of PKC) significantly but partially inhibited the PDBu-induced BSM contraction during K + stimulation. GF109203X (an inhibitor of PKCs , β, , and ) 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.