Effect Of 2-phenacyl-4H-1, 4-benzothiazin-3-one On The Action Potentials In Papillary Muscle And Sinoatrial Node Of Guinea Pig

Calcium channel blockers are most commonly used to treat cardiovascular diseases such as hypertension, angina pectoris and cardiac arrhythmia and so on. Currently, CCBs obtain considerable development through the study of structure-activity relationship of original calcium antagonists. Benzothiazepine blocked calcium channel with a high selectivity. Diatiezem, the representative of benzothiazepine, was widely used in cardiovascular diseases without tolerance and significant side effects. We had knowledge of their structure-activity relationship, but a few analogues were listed as drugs. Clentiazem, with the same parent structure (1,5-benzothiazepine-4-one) with benzothiazepine, was used as a vasodilator. Semotiadil, with 1, 4-benzothiazin-3-one structure, was a new type of L-type voltage-dependent calcium channel blocker. The compound (2-phenacyl-4H-1, 4-benzothiazin-3-one, PBT for short) studied in this experiment had similar chemical structure with semotiadil. It is unclear whether PBT can also block calcium channel. Drugs enumerated above acted selectivity on cardiac muscle, so we carried out this experiment to observe the effect of PBT on cardiac muscle. Cardiovascular system mainly existed L-type and T-type voltage-gated calcium channels. L-type calcium channel distributed in the cell membrane on the cardiovascular system with a high-density and was the most important way of the extracellular calcium influx when cells were excited. T-type calcium channel mainly distributed in conduction and pacemaker cells, whereas ventricular myocytes had little or did not exist. It was activated at a relatively low voltage and inactivated fast. It played a small role in the formation of cardiac action potential but mainly participated in the regulation of cardiac automaticity and vascular tension.The effects of PBT on the action potentials in papillary muscle cells and pacemaker cells in sinoatrial node of guinea pig in vitro were observed in this experiment using the standard glass microelectrode technique.Part.1 Effect of 2-phenacyl-4H-1, 4-benzothiazin-3-one on the action potential in papillary muscle of guinea pig Aim: To observe the effect of PBT on the action potential in papillary muscle of guinea pig and analyze the possible mechanisms.Methods: (1) The normal papillary muscle: The standard glass microelectrode technique was used to record the action potential in papillary muscle of guinea pig. The action potentials were observed and recorded under square-wave stimulation with 1 Hz stimulation frequency and 1.5 times of the threshold. They included the action potentials before and after administration of PBT (1μM, 3μM, 10μM and 30μM). Then the action potential parameters were analyzed, which included action potential amplitude (APA), resting potential (RP), overshoot (OS), maximal rate of 0 phase depolarization (Vmax), duration of 30% repolarization (APD30), duration of 50% repolarization (APD50), duration of 90% repolarization (APD90). 0.1% DMSO/K-H solution was applied as the parallel solvent control. (2) The partially depolarized papillary muscle: The stable partially depolarized action potentials were triggered through circulation perfusion for 20 minutes with high K + K-H solution. And the action potential parameters were recorded and analyzed by the same way as action potential in normal papillary muscle before and after administration of PBT (10μM).Results: (1) In the normal papillary muscle PBT (1μM, 3μM, 10μM and 30μM) shortened APD30, APD50 and APD90 (P<0.05), but had no significant effect on APA, RP, OS and Vmax at this concentration range (P>0.05). Solvent had no effect on the parameters of action potential (P>0.05). (2) In partially depolarized papillary muscle, PBT (10μM) shortened APD30 (P<0.05), APD50 and APD90 (P<0.01) and reduced APA and Vmax (P<0.05). Solvent had no effect on the parameters of action potential (P>0.05).Conclusion: The compound 2-phenacyl-4H-1, 4-benzo- thiazin-3-one shortened APD in papillary muscle of guinea pig, decreased APA and Vmax in partially depolarized papillary muscle. It's inferred that this compound affected the action potential of papillary muscle of guinea pig by inhibiting Ca2 + influx.Part.2 Effect of 2-phenacyl-4H-1, 4-benzothiazin-3-one on the action potential in pacemaker cells in sinoatrial node of guinea pigAim: To observe the effect of PBT on the action potential in pacemaker cells in sinoatrial node of guinea pig and analyze the possible mechanisms.Methods: The standard glass microelectrode technique was used to record the action potential in pacemaker cells in sinoatrial node of guinea pig before and after administration of PBT (1μM, 3μM, 10μM and 30μM). Then the action potential parameters were analyzed, which included maximal diastolic potential (MDP), OS, APA, velocity of 4 phase depolarization (V4), Vmax, APD30, APD50, APD90 and rate of pacemaker firing (RPF). 0.1% DMSO/K-H solution was applied as the parallel solvent control.Results: PBT (1μM, 3μM, 10μM and 30μM) reduced Vmax, V4 and RPF in a concentration-dependent manner (P<0.05), and significantly reduced APA (P<0.05). PBT (1μM, 3μM and 10μM) had no significant effect on APD30, APD50 and APD90 (P>0.05), whereas PBT (30μM) significantly prolonged APD90 (P<0.05). However, it had no significant effect on RP and OS at the concentration range (P>0.05). Solvent had no effect on the parameters of action potential (P>0.05).Conclusion: The compound 2-phenacyl-4H-1, 4-benzo- thiazin-3-one reduced V4 and Vmax, lowered RPF and prolonged the repolarization time in pacemaker cells in sinoatrial node of guinea pig. These effects may be attributed to the inhibition of the influx of the extracellular calcium and the efflux of the intracellular potassium.