Chan Yau-Chi, Siu Chung-Wah, Lau Yee-Man, Lau Chu-Pak, Li Ronald A, Tse Hung-Fat
Cardiology Division, Department of Medicine, University of Hong Kong, Hong Kong.
J Cardiovasc Electrophysiol. 2009 Sep;20(9):1048-54. doi: 10.1111/j.1540-8167.2009.01475.x.
Normal heart rhythms originate in the sinoatrial node. HCN-encoded funny current (I(f)) and the Kir2-encoded inward rectifier (I(K1)) counteract each other by respectively oscillating and stabilizing the negative resting membrane potential, and controlling action potential firing. Therefore, I(K1) suppression and I(f) overexpression have been independently exploited to convert cardiomyocytes (CMs) into AP-firing bioartificial pacemakers. Although the 2 strategies have been largely assumed synergistic, their complementarity has not been investigated.
We explored the interrelationships of automaticity, I(f) and I(K1) by transducing single left ventricular (LV) CMs isolated from guinea pig hearts with the recombinant adenoviruses Ad-CMV-GFP-IRES-HCN1-AAA and/or Ad-CGI-Kir2.1 to mediate their current densities via a whole-cell patch clamp technique at 37 degrees C. Results showed that Ad-CGI-HCN1-AAA but not Ad-CGI-Kir2.1 transduction induced automaticity (181.1 +/- 13.1 bpm). Interestingly, Ad-CGI-HCN1-AAA/Ad-CGI-Kir2.1 cotransduction significantly promoted the induced firing frequency (320.0 +/- 15.8 bpm; P < 0.05). Correlation analysis revealed that the firing frequency, phase-4 slope and APD(90) of AP-firing LV CMs were correlated with I(f) (R(2) > 0.7) only when -2 >I(K1) >-4 pA/pF but not with I(K1) over the entire I(f) ranges examined (0.02 < R(2) < 0.4). Unlike I(f), I(K1) displayed correlation with neither the phase-4 slope (R(2)= 0.02) nor phase-4 length (R(2)= 0.04) when -2 > I(f) > -4 pA/pF. As anticipated, however, APD(90) was correlated with I(K1) (R(2)= 0.4).
We conclude that an optimal level of I(K1) maintains a voltage range for I(f) to operate most effectively during a dynamic cardiac cycle.
正常心脏节律起源于窦房结。由HCN编码的超极化激活的阳离子电流(I(f))和由Kir2编码的内向整流钾电流(I(K1))通过分别使静息膜电位振荡和稳定以及控制动作电位发放来相互拮抗。因此,I(K1)抑制和I(f)过表达已被分别用于将心肌细胞(CMs)转化为能发放动作电位的生物人工起搏器。尽管这两种策略在很大程度上被认为具有协同作用,但它们的互补性尚未得到研究。
我们通过用重组腺病毒Ad-CMV-GFP-IRES-HCN1-AAA和/或Ad-CGI-Kir2.1转导从豚鼠心脏分离的单个左心室(LV)心肌细胞,在37℃下通过全细胞膜片钳技术调节其电流密度,从而探究自律性、I(f)和I(K1)之间的相互关系。结果显示,Ad-CGI-HCN1-AAA转导而非Ad-CGI-Kir2.1转导诱导了自律性(181.1±13.1次/分钟)。有趣的是,Ad-CGI-HCN1-AAA/Ad-CGI-Kir2.1共转导显著提高了诱导的发放频率(320.0±15.8次/分钟;P<0.05)。相关性分析表明,仅当-2>I(K1)>-4 pA/pF时,发放动作电位的LV心肌细胞的发放频率、4期斜率和动作电位时程(APD(90))与I(f)相关(R(2)>0.7),而在整个检测的I(f)范围内(0.02<R(2)<0.4)与I(K1)无关。与I(f)不同,当-2>I(f)>-4 pA/pF时,I(K1)与4期斜率(R(2)=0.02)和4期长度(R(2)=0.04)均无相关性。然而,正如预期的那样,APD(90)与I(K1)相关(R(2)=0.4)。
我们得出结论,在动态心动周期中,I(K1)的最佳水平维持了I(f)最有效发挥作用的电压范围。