Lieu Deborah K, Chan Yau Chi, Lau Chu Pak, Tse Hung Fat, Siu Chung Wah, Li Ronald A
Stem Cell Program, University of California, Davis, California, USA.
Heart Rhythm. 2008 Sep;5(9):1310-7. doi: 10.1016/j.hrthm.2008.05.010. Epub 2008 May 15.
Current strategies of engineering bioartificial pacemakers from otherwise silent yet excitable adult atrial and ventricular cardiomyocytes primarily rely on either maximizing the hyperpolarization-activated I(f) or on minimizing its presumptive opponent, the inwardly rectifying potassium current I(K1).
The purpose of this study was to determine quantitatively the relative current densities of I(f) and I(K1) necessary to induce automaticity in adult atrial cardiomyocytes.
Automaticity of adult guinea pig atrial cardiomyocytes was induced by adenovirus (Ad)-mediated overexpression of the gating-engineered HCN1 construct HCN1-DeltaDeltaDelta with the S3-S4 linker residues EVY235-7 deleted to favor channel opening.
Whereas control atrial cardiomyocytes remained electrically quiescent and had no I(f), 18% of Ad-CMV-GFP-IRES-HCN1-DeltaDeltaDelta (Ad-CGI-HCN1-DeltaDeltaDelta)-transduced cells demonstrated automaticity (240 +/- 14 bpm) with gradual phase 4 depolarization (143 +/- 28 mV/s), a depolarized maximal diastolic potential (-45.3 +/- 2.2 mV), and substantial I(f) at -140 mV (I(f,-140 mV) = -9.32 +/- 1.84 pA/pF). In the remaining quiescent Ad-CGI-HCN1-DeltaDeltaDelta-transduced atrial cardiomyocytes, two distinct immediate phenotypes were observed: (1) 13% had a hyperpolarized resting membrane potential (-56.7 +/- 1.3 mV) with I(f,-140 mV) of -4.85 +/- 0.97 pA/pF; and (2) the remaining 69% displayed a depolarized resting membrane potential (-27.6 +/- 1.3 mV) with I(f,-140 mV) of -23.0 +/- 3.71 pA/pF. Upon electrical stimulation, both quiescent groups elicited a single action potential with incomplete phase 4 depolarization that was never seen in controls. Further electrophysiologic analysis indicates that an intricate balance of I(K1) and I(f) is necessary for induction of atrial automaticity.
Optimized pacing induction and modulation can be better achieved by engineering the I(f)/I(K1) ratio rather than the individual currents.
目前从原本静止但可兴奋的成年心房和心室心肌细胞构建生物人工起搏器的策略主要依赖于最大化超极化激活的I(f)或最小化其假定的对手——内向整流钾电流I(K1)。
本研究的目的是定量确定诱导成年心房心肌细胞自律性所需的I(f)和I(K1)的相对电流密度。
通过腺病毒（Ad）介导的门控工程化HCN1构建体HCN1-ΔΔΔ的过表达诱导成年豚鼠心房心肌细胞的自律性，其中S3-S4连接子残基EVY235-7缺失以促进通道开放。
对照心房心肌细胞保持电静止且无I(f)，而18%的Ad-CMV-GFP-IRES-HCN1-ΔΔΔ（Ad-CGI-HCN1-ΔΔΔ）转导细胞表现出自律性（240±14次/分钟），伴有逐渐的4期去极化（143±28 mV/s）、去极化的最大舒张电位（-45.3±2.2 mV）以及在-140 mV时显著的I(f)（I(f,-140 mV)=-9.32±1.84 pA/pF）。在其余静止的Ad-CGI-HCN1-ΔΔΔ转导的心房心肌细胞中，观察到两种不同的即时表型：（1）13%的细胞静息膜电位超极化（-56.7±1.3 mV），I(f,-140 mV)为-4.85±0.97 pA/pF；（2）其余69%的细胞静息膜电位去极化（-27.6±1.3 mV），I(f,-140 mV)为-23.0±3.71 pA/pF。电刺激时，两个静止组均引发单个动作电位，伴有不完全的4期去极化，这在对照组中从未见过。进一步的电生理分析表明，I(K1)和I(f)的复杂平衡对于诱导心房自律性是必要的。
通过设计I(f)/I(K1)比值而非单个电流，可以更好地实现优化的起搏诱导和调节。
