Effects of melittin on isolated papillary muscles of guinea pig

AIM: To investigate the effect of melittin (Mel) on papillary muscles of gu inea pigs. METHODS: Contraction of papillary muscles were examined by conve ntional method and action potentials (AP) were recorded by standard glass m icroelectrode technique. RESULTS: Mel (0.5, 3 mu mol/L) significantly incre ased the contractility of guinea pig papillary muscles while 5 mu mol/L exe rted dual action with a transient decrease followed by an increase of the c ontractility. Mel shortened the functional refractory period (FRP) at conce ntrations of 0.5, 3, and 5 mu mol/L and increased the automaticity induced by adrenaline (Adr) at 3 and 5 mu mol/L. Met shifted the duration-intensity curve upward at 3 mu mol/L. It shortened the action potential duration (AP D) of fast action potential (FAP), decreased the action potential amplitude (APA) and resting potential (RP) at 0.5 and 3 mu mol/L. As to slow action potential (SAP), Mel 0.8 mu mol/L shortened APD(20) and APD(50), and decrea sed ARA and RP. CONCLUSION: Mel increased the contractility and automaticit y of papillary muscles, shortened the FRP, decreased the excitability, shor tened the APD, and decreased APA and RP of AP.