Fig. 5. Dose–response relationship of halothane on phorbol-12,13-dibutyrate (PDBu)-induced force. Mean ± SD (n = 3); PDBu = a PKC activator in the presence of pCa 6.7; PDBu-induced force after administration of halothane at peak force (A , peak contraction) or 30 min (B , late relaxation) expressed as percent of the control force (steady state force before the administration of halothane); *=P < 0.05 compared to 0% halothane. Halothane, at 3%, significantly increased the PDBu-induced force (A , peak contraction) and dose-dependently decreased the force (B , late relaxation) up to 2% halothane. No further decrease in PDBu-induced force was observed by 3% halothane.