Blocking Effects Of Ligustrazine And Nitrate Ketone Derivatives On Pacemaker Currents (If) In Sinoatrial Node Cells And HCN4Channels

Aim: The objectives of this study were to investigate the inhibitory effects ofLigustrazine（TMP）and nitrate ketone derivative (TBN) on HCN4participationcoding hyperpolarization activated cyclic nucleotide gated cation channels current (If)and action potential (AP) in rabbit sinoatrial node cell.Methods: HCN4channels expressed in Xenopus laevis oocytes and actionpotential (AP) in rabbit sinoatrial node cells were recorded by means of standardtwo-microelectrode voltage-clamp technique and glass microelectrode technique.Results: HCN4is blocked in a concentration-and voltage-dependent manner byTMP and TBN(TMP: half-maximal inhibition concentration [IC50]=48.79±3.1μmol/L; TBN:[IC50]=17.20±1.1μmol/L). In addition, the results of rabbit sinoatrialnode action potential experiments showed that DDR in sinoatrial node myocytes wasslowed after giving100μmol/L TMP and TBN, with the DDR of TMP and TBN slowingfrom(19.53±1.2) to (13.79±1.0) and (21.16±1.4) to (7.10±1.9) mV/s(n=6，P<0.01).Another experiments that give100μM H2O2, the DDR obviously increasedfrom (20.98±1.28) to(33.24±2.3) and (21.66±1.1) to (35.71±2.1) mV/s(n=6，P<0.01). After adding100μmol/L TMP and TBN, the DDR decreased to (23.57±2.44)and (12.27±2.23) mV/s(n=6，P<0.01).Conclusion: TMP and TBN has obvious inhibitory effect on rabbit spontaneousrate in sinoatrial node cells and the hyperpolarization activated cation channel current(If) whicn was expressed in the Xenopus oocyte and coded by HCN4,and also canreduce100μM H2O2induced increase of sinoatrial node phase-4spontaneousdepolarization rate (DDR) and the blocking effect of TBN obviously stronger than themother nucleus structure TMP. At the same time，we also found that after giving300μM H2O2can lead to cardiac arrhythmia, and100μM TBN can reverse this effect.The above results suggest that TMP and TBN might have a certain amount of clinicalreference value for primary sinus tachycardia or sinoatrial node quickness arrhythmiainduced under pathological conditions. Aim: The objectives of this study were to investigate the inhibitory effects of Ligustrazine（TMP）and nitrate ketone derivative (TBN) on HCN4participation coding hyperpolarizationactivated cyclic nucleotide gated cation channels current (If) and action potential (AP) in rabbitsinoatrial node cell.Methods: HCN4channels expressed in Xenopus laevis oocytes and action potential (AP) inrabbit sinoatrial node cells recorded by means of standard two-microelectrode voltage-clamptechnique and glass microelectrode technique.Results: HCN4is blocked in a concentration-and voltage-dependent manner by TMP andTBN(TMP: half-maximal inhibition concentration [IC50]=48.79±3.1μmol/L; TBN:[IC50]=17.20±1.1μmol/L). In addition, the results of rabbit sinoatrial node action potentialexperiments showed that DDR in sinoatrial node myocytes was slowed after giving100μmol/L TMP and TBN,with the DDR of TMP and TBN slowing from(19.53±1.2) to(13.79±1.0) and (21.16±1.4) to (7.10±1.9) mV/s(n=6，P<0.01).Another experiments thatgive100μM H2O2, the DDR obviously increased from (20.98±1.28) to(33.24±2.3) and(21.66±1.1) to (35.71±2.1) mV/s(n=6，P<0.01). After adding100μmol/L TMP and TBN, theDDR decreased to (23.57±2.44) and (12.27±2.23) mV/s(n=6，P<0.01).Conclusion:（1）TMP and TBN has obvious inhibitory effect on rabbit spontaneous nodephase-4spontaneous depolarization rate (DDR) and the hyperpolarization activated cationchannel current (If) whicn was expressed in the Xenopus oocyte and coded by HCN4;（2）TMP and TBN can reduce100μM H2O2induced increase of sinoatrial node phase-4spontaneous depolarization rate (DDR);（3） The blocking effect of TBN obviously strongerthan the mother nucleus structure TMP;（4）300μM H2O2can lead to cardiac arrhythmia, and 100μM TBN can reverse this effect. The above results suggest that TMP and TBN might havea certain amount of clinical reference value for primary sinus tachycardia or sinoatrial nodequickness arrhythmia induced under pathological conditions.