异丙肾上腺素诱导钙离子激活氯电流在兔心房肌细胞电重构中的意义

The role of isoprenaline-induced, calcium-activated transient outward chloride current in atrial electrical remodeling of rabbit

目的探讨在异丙肾上腺素(ISO)诱导下,兔心房肌细胞L型钙电流(ICa,L)与钙离子激活氯电流(ICl,Ca)之间的变化以及心房肌细胞动作电位(AP)复极相的特征性变化。方法用酶解法分离兔心房肌细胞。全细胞膜片钳技术记录所需离子电流和AP。结果(1)在记录到ICa,L后,加入1μmol/LISO5min,可引出一个非常明显的外向电流,并随着钳制电压的增加,ICa,L峰值逐步减小,而外向电流峰值逐步增加。3mmol/L的4氨基吡啶对这种外向电流不起作用。但150μmol/L的4,4异二硫氮氐2,2′二磺酸可抑制这种外向电流,而几乎只剩下ICa,L。200μmol/L钙通道阻滞剂CdCl2可阻断ICa,L和外向电流。表明该实验在加入ISO后引出最初的内向电流ICa,L之后,被激活的外向电流为ICl,Ca,诱发率为91.67%(P<0.05)。(2)在电流钳制下引出AP后,1μmol/LISO可使正常情况下的AP平台没有,AP呈三角形的尖锥峰形。AP时程的APD50和APD90明显缩短,与对照组相比,分别缩短了80.46%和71.87%,差异有统计学意义。3mmol/L的4氨基吡啶对该AP三角形的尖锥峰几乎没有作用;但4,4异二硫氮氐2,2′二磺酸(150μmol/L)使AP平台得以恢复,与对照组相比,差异无统计学意义。表明正常的心房肌细胞在ISO作用下,与形成AP复极相有关的1相和2相的离子转运发生了改变,Ito2对心房肌细胞AP1相形成起着重要作用。结论兔心房肌细胞在原本只被记录ICa,L情况下,经ISO干预后,细胞内某离子浓度发生了改变,细胞膜上离子通道的开放发生了重新变化,钙离子激活Cl-通道,Ito2表现出了明显优势,使AP时程明显缩短,AP呈三角形的尖锥峰形而无明显平台,心房肌细胞发生了离子通道电重构。离子通道电重构可能起自于ISO诱导的L型钙通道激活氯离子通道开放增加,并且ICa,L降低。这可能揭示离子通道电重构发生的一种机制。也为探讨实验性房性心律失常发生机制提供了又一证据。

Objective To investigate the relationship between the changes of the L-type calcium current （ICa,L） and the calcium-activated transient outward chloride current （ICa.Ca）, and the repolarization characteristic of action potential in phase 1 under isoprenaline （ ISO ） stimulation in atrium myocytes of rabbit. Methods Atrium myocytes were obtained by enzymatic dissociation from a section of atrial free wall. The membrane currents and action potential were recorded by the whole-cell patch-clamp technique. Results After recording ICa,L ,atrium myocytes were perfused with ISO（ 1 μmol/L） immediately. Five minutes later, a transient outward current（ Ito ） was significantly induced, and the peak of Ito was gradually increased while ICa.,L gradually decreased with increasing in clamp voltage. The Ito was resistant to 4-AP （3 mmol/L） but sensitive to DIDS （150 μmol/L, C1- channel blocker）. This current was blocked by CdC12 （200 μmol/L, Ca^2＋ channel blocker）. The elicited rate of Ito was 91.67% （ P 〈 0. 05 ）. （2） The shape of AP was like an inverse triangle with no plateau in Phase 2 after ISO （ 1 μmol/L） perfusion. Moreover, compared to the parameters of control group, APDs0 and APDg0 were significantly shortened from （65.4 ± 4. 2） ms and （95.8 ±3.8）ms to（ 12. 8 ±3.8）ms and（27, 0 ±4. 7）ms, and reduced to 80. 46% and 71.87% , respectively （P 〈0. 01 ,n = 12）. 4-AP （3 mmol/L） had on obvious effect on the shape of AP, however, the plateau of AP in phase 2 was recovered by DIDS（ 150 μmol/L）perfusion, APD50 and APDg0 were （41. 1 ± 4.5 ）ms and （79. 6± 3.4 ） ms respectively. Compared to the parameters of control group, there were no significant differences （P 〉0. 05 ,n = 12）. These results indicated that ionic transport were changed by ISO perfusion in atrium myocytes and Ito played an important role in the phase 1 repolarization of AP. Conclusions Before ISO administration, we could only observe I Ca.L in atrium myocytes of rabbit . After isoproterenal intervention, certain intracellular ionic consistence and membrane ionic channels were changed. Calcium activated chloride channel and Ito2 revealed obvious predominance which shorten APD significantly. Action potential showed a triangle with no plateau, suggesting an electrical remodeling in atrium myocytes. The remodeling of ionic channel is related possibly with the opening of Ca^2＋ -activated Cl^- current, which maybe the electrophysioliogical base of reentrant atrial tachycardia.