压力负荷性心衰小鼠左心室跨壁L-型钙电流的变化

Transmural L-type calcium current in a pressure-overloaded mouse model with heart failure

为了观察正常和心衰时心内膜下和心外膜下心肌细胞L-型钙电流(ICa-L)的差别,我们采用主动脉弓狭窄的方法建立小鼠压力超负荷性心衰模型,采用全细胞膜片钳技术记录了正常、主动脉狭窄(band)及假手术对照(sham)组动物左心室游离壁内、外膜下心肌细胞的动作电位时程(action potential duration,APD)和ICa-L。结果显示:(1)与sham组同龄的正常小鼠左心室心内膜下细胞动作电位复极达90％的时程(APD90)为(38．2±6．44)ms,较心外膜下细胞的APD90(15.67±5.31)ms明显延长,二者的比值约为2．5:1;内膜下细胞和外膜下细胞ICa-L密度没有差异,峰电流密度分别为(-2.7±0.49)pA/pF和(-2.54±0．53)pA/pF;(2)Band组内、外膜下细胞的动作电位复极达50％的时程(APD50)、APD90均较sham组显著延长,尤以内膜下细胞延长突出,分别较sham组延长了400％和360％,内、外膜下细胞APD90的比值约为4.2:1;(3)与sham组相比, band组内膜下细胞ICa-L密度显著减小,在+10 mV～+40 mV的4个电压下分别降低了20．2％、21．4％、21.6％和25.7％(P< 0．01),但其激活电位、峰电位和翻转电位没有改变;band组外膜下细胞的ICa-L密度与同期sham组相比无明显变化;band组钙通道激活、失活及复活的动力学特征与sham组相比没有改变。以上结果提示,生理状态下小鼠左心室内、外膜下细胞ICa-L密度不存在明显差别,提示ICa-L与APD跨壁异质性的产生无关;心衰时左心室内、外膜下细胞APD明显延长,以内膜下细胞延长尤为突出,内膜下细胞ICa-L密度明显减少,而外膜下细胞ICa-L密度无明显改变,这种ICa-L的非同步变化在心衰时可能起到对抗APD延长、减少复极离散度的有益作用。

Transmural electrical heterogeneity plays an important role in the normal dispersion of repolarizaion and propagation of excitation in the heart. The amplification of transmural electrical heterogeneity contributes to the genesis of arrhythmias in cardiac hypertrophy and failure. We established a mouse model with cardiac failure by aortic handing and investigated the possible contribution of L-type calcium current （ICa-L） to transmural electrical heterogeneity in both normal and failing hearts. Single myocytes were enzymatically isolated from suhendocardial and suhepicardial myocardium of the free left ventricle wall. The recordings of action potential and ICa-L were performed using the conventional whole-cell patch-clamp technique. The results showed that： （1） The action potential duration at 90% repolarization （APD90） of the suhendocardial myocytes in normal control mice was （38.2±6.44） ms, which was significantly longer than that of the suhepicardial myocytes [（15.67±5.31） ms]. The ratio of APD90 for suhendocardial/suhepicardial myocytes was about 2.5：1. The peak ICa-L density in subendocardial myocytes was （-2.7±0.49） pA/pF, which was not different from that in suhepicardial myocytes [（-2.54±0.53） pA/pF]. （2） In failing hearts, both action potential duration at 50% repolarization （APD90） and APD90 were remarkably prolonged either in suhendocardial or subepicardial myocytes compared to that in sham hearts. The subendocardial myocytes had much longer APD. The ratio of APD00 for subendocardial/subepicardial myocytes changed to about 4.2：1. （3） ICa-L density in subendocardial myocytes was significantly decreased in failing hearts compared with that in sham hearts. At four test potentials from ＋ 10 mV to ＋40 mV, the density of ICa-L from subendocardial myocytes in failing hearts was decreased by 20.2%, 21.4%, 21.6% and 25.7%, respectively （P〈0.01）. However, no significant difference was observed in ICa-L density from subepicardial myocytes in failing hearts. There was no significant difference in the kinetic properties of ICa-L in subendocardial and subepicardial myocytes between the band and sham groups. We conclude that ICa-L may not contribute to the physiological transmural electrical heterogeneity in mouse hearts. The electrical heterogeneity is exaggerated and the density of ICa-L is decreased in the subendocardial myocytes, but not in the subepicardial myocytes in failing hearts. The results obtained suggest that the decreased density of ICa-L in subendocardial myocytes is POssibly an adaptive response to the prolongation of action potential due to delayed depolarization and may reduce the transmural dispersion of repolarization in heart failure.