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