Na+/Ca2+交换体电流在兔左心室壁分布的异质性

目的探讨Na+/Ca2+交换体电流(INa+/Ca2+)在左室肌不同部位的分布特征及其与跨壁复极异质性的关系.方法采用全细胞膜片钳技术,分别记录兔左心室肌内膜下、中层及外膜下细胞的动作电位(AP)、INa+/Ca2+及IK.结果中层细胞AP时程明显长于外膜下细胞(P<0.01);在+40 mV时,外向INa+/Ca2+密度在中层细胞明显大于外膜下及内膜下细胞(P分别＜0.01,0.05);在-100 mV时,内向INa+/Ca2+密度在中层细胞明显大于外膜下(P<0.05);在测试电压为+50mV时,中层细胞的IKs尾电流密度明显小于外膜下细胞(P<0.05), 内膜下、中层及外膜下细胞的IKr尾电流密度无明显区别(P>0.05).结论 INa+/Ca2+与IKs在兔左室肌的分布具有异质性,并导致了跨壁复极异质性的形成.

Heterogeneity of Na+/Ca2+ Exchanger Current Across the Left Ventricular Wall of Rabbit

Objective To investigate the distribution characteristics of Na +/Ca 2+ exchanger current (I Na +/Ca 2+ ) across the left ventricular wall of rabbit and the relationship between I Na +/Ca 2+ and transmural depolarization heterogeneity. Methods By using whole cell patch clamp techniques, action potentials(AP), I Na +/Ca 2+ , and both rapid and slow components of delayed rectifier potassium current(I Kr and I Ks ) were recorded in subendocardial(Endo), midmyocardial(M), and subepicardial(Epi) cells of the left ventricular wall of rabbit. Results AP duration in M cells was longer than that in Epi cells, P <0.01. At the test potential of +40 mV, outward I Na +/Ca 2+ in M cells was larger than that in Epi and Endo cells, P <0.01, P <0.05, respectively. At the test potential of -100 mV, inward I Na +/Ca 2+ in M cells was larger than that in Epi cells, P <0.05. At the test potential of +50 mV, the tail current density of I Ks in M cells was smaller than that in Epi cells, P <0.05, and there was no significant difference among the tail current densities of I Kr in Endo, M, and Epi cells. Conclusion The distribution of I Na +/Ca 2+ and I Ks across the left ventricular wall of rabbit is unequal, which contributes to the transmural depolarization heterogeneity.