Effects Of Tutin On Action Potentials Of Papillary Muscles In Guinea Pig

Coriaria sinica Maxim is a bush of Coriaria L,it includes about 15 species in the world. In china, It is a wild plant and includes 3 species in China. It is used as an anti-flammary agent and a pesticide in the folk. It has been studied since 1970s. Riban separated a chemical component from Coriaria myrtifolia which can cause epilepsy at the first time in 1964. Coriaria sinica Maxim has plentiful pharmacological action: (1) It is used to prevent all kinds of noxious insects, as a pesticide in the folk long time ago; (2)It can be used to cure cancer. Scientis have seperated a tannin component -coriamyrtin A from Coriaria sinica Maxim which can be used as an anticancer drugs; (3)It has distinguished pharmacological action on central nerve, and it is used to cure schizophrenia and induce epileptic animal models. Coriaria sinica Maxim contains many poisonous components and it can cause intoxication after eating by mistake.The present work was undertaken to study the effects of tutin, a kind of component extracted from Coriaria sinica Maxim, on action potential (AP) in isolated guinea pig papillary muscles by using conventional intracellular microelectrode technique, and further analyze the possible mechanisms.We elicit fast action potential(FAP) by using a standard miocroelectrode and started recording the result of experiment after impalement was stabilized for 30 minutes; For slow action potential(SAP), after impalement was stabilized for 30 minutes,high K⁺(25mmol/L) Tyrode solution was prepared by equitable substitution of KCl for NaCl,containing isoprenaline (1μmol/L )and VitC(4μmol/L)or BaCl₂(0.2mmol/L)to elicit SAP after depolarization of the. resting potential and inaction of fast Na⁺ channels. Experiments started after the recording of control SAP for 30 minutes.Data of and APs parameters were presented as the mean±SE. And the difference within a group was evaluated by student t test; variation among groups were evaluated by one-way ANOVA analyse, followed by F test. While p value less than 0.05 was considered significant.Results1. Effects of tutin on fast action potential recorded from guinea-pig papillary musclesWith a perfusion of tutin at concentrations from 0.01μmol/L to 100μmol/L, both APD₅₀ and APD₉₀ were prolonged in concentration dependent manner. While, the RP, APA, V_max were not affected obviously at any used concentrations. When the concentration is higher than 0.1μmol/L, as compare to the control, prolongation of APD₅₀ and APD₉₀ induced by tutin was significant difference (P<0.05). At concentration of 1000μmol/L, the graph of FAP chagned. At concentration of 100μmol/L, The changes in APD were observed after pretreating the muscle with 1μM nimodipine, both APD₅₀ and APD₉₀ were decreased ( P<0.05).2. Effects of E-4031 and nimodipine on prolonged APD induced by tutin in guinea-pig papillary musclesPretreating the papillary muscle with 10μmol/L E-4031 and 1μmol/L nimodipine, followed by perfusion of tutin with a concentration of 10μmol/L, both APD₅₀ and APD₉₀ did not change obviously (P>0.05), indicating no blockade of I_Ks by pretreatment of E-4031 and nimodipine.3. Effects of chromanol 293B and nimodipine on prolonged APD induced by tutin in guinea-pig papillary musclesFurthermore, pretreating the papillary muscle with 10μmol/L 293B and 1μnol/L nimodipine, followed by perfusion of tutin with a concentration of 10μmol/L, both APD₅₀ and APD₉₀ did not change obviously (P>0.05). This indicated no blockade of I_Kr by pretreatment of chromanol 293B and nimodipine.4. The frequency dependence of APD prolongation caused by tutinThe APD was also measured at different BCL (varied from 1s, 2s and 5s repectively) in the presence of 10μmol/L of tutin. With the increase of BCL, both APD50 APD90 tended to became shortened but no marked difference as compare to control. This demonstrated that the effect of tutin on APD is frequency independent.5. Effects of tutin on slow action potential induced by isoprenaline inguinea-pig papillary musclesTutin at 10μmol/L significantly increased the APA,V_max, APD₅₀ as well as APD₉₀ of SAP as compare to the control (P<0.05), but have no effect on RP.6. Effects of tutin on slow action potential induced by BaCl₂ inguinea-pig papillary musclesSimilarly, tutin at 10μmol/L significantly increased the APA,V_max, APD₅₀, and APD₉₀ of SAP ( P<0.05) but no obvious effect on RP (P>0.05).In conclusions:1. Tutin can prolong APD in fast action potential in guinea pigs papillary muscle in a concentration-dependent manner,and this effect can be suppressed by nimodipine (a Ca²⁺ channel blocker);2. E-4031(a I_Kr blocker) and chromanol 293B (a I_Ks blocker) can not affect prolonged APD induced by tutin in guinea-pig papillary muscles. This indicated the prolonged effect by tutin had no communination with I_Kr and I_Ks channels;3. The prolongation of APD caused by tutin was frequency-independent;4. Tutin can increase APA, V_max, APD₅₀, APD in slow action potential in guinea-pig papillary muscles, and this effect can be suppressed by nimodipine;5. In consequence we can conclusion: Tutin can provok Ca²⁺ channel. Maybe be it is a calcium channel antagonist.