Integrated allosteric model of voltage gating of HCN channels
Integrated allosteric model of voltage gating of HCN channels
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DOI：
10.1085/jgp.117.6.519
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发表时间：
2001-06-01
影响因子：
3.8
通讯作者：
DiFrancesco, D
中科院分区：
文献类型：
--
作者：
Altomare, C;Bucchi, A;DiFrancesco, D
超极化激活(起搏器)通道由负电压和细胞内cAMP双重调节。天然心脏f通道的动力学与HII门控不兼容，需要闭合/开放的多状态模型。我们证实了HCN通道家族的成员(mHCN1，hHCN2，hHCN4)也具有不符合WH门控的特性，如S形激活和去激活，激活偏离指数的固定幂，通过预适应超极化消除激活的“延迟”。以往对天然通道的研究表明，cAMP在开放概率(Po)曲线上的移动作用可以用变构模型来解释，即cAMP更有利于与开放的通道结合。因此，我们询问，超极化激活通道不仅依赖于cAMP，而且依赖于电压的门控是否可以用变构模型来解释。我们假设HCN通道是四聚体，并且每个子单元包括一个在不情愿和愿意之间移动的电压传感器，而电压传感器独立地被电压选通，通道闭合/开放转换发生变构。这些假设导致了一个包括五个开放和五个闭合通道状态的多态方案。我们通过先拟合激活延迟曲线和单指数时间常数曲线，然后再拟合单独的激活/失活轨迹来估计模型速率常数。通过简单地使用不同的速率常数，该模型解释了所研究的所有三种HCN异构体的电压门控的定性和定量方面，并允许解释不同异构体的不同动力学性质。例如，与HCN1/HCN4相比，HCN1的动力学速度更快是由于更高的HCN1电压传感器的速率和闭合/开放转变中亚基之间较松散的电压无关相互作用。还解释了传感器正电荷的减少导致Po曲线的电压负移，而曲线斜率变化不大的实验证据。因此，HCN电压门控包括两个过程：电压传感器门控和变构开启/关闭。
Hyperpolarization-activated (pacemaker) channels are dually gated by negative voltage and intracellular cAMP. Kinetics of native cardiac f-channels are not compatible with HII gating, and require closed/open multistate models. We verified that members of the HCN channel family (mHCN1, hHCN2, hHCN4) also have properties not complying with WH gating, such as sigmoidal activation and deactivation, activation deviating from fixed power of an exponential, removal of activation "delay" by preconditioning hyperpolarization. Previous work on native channels has indicated that the shifting action of cAMP on the open probability (Po) curve can be accounted for by an allosteric model, whereby cAMP binds more favorably to open than closed channels. We therefore asked whether not only cAMP-dependent, but also voltage-dependent gating of hyperpolarization-activated channels could be explained by an allosteric model. We hypothesized that HCN channels are tetramers and that each subunit comprises a Voltage sensor moving between "reluctant" and "willing" states, whereas voltage sensors are independently gated by voltage, channel closed/open transitions occur allosterically These hypotheses led to a multistate scheme comprising five open and five closed channel states. Wie estimated model rate constants by fitting first activation delay curves and single exponential time constant curves, and then individual activation/deactivation traces. By simply using different sets of rate constants, the model accounts for qualitative and quantitative aspects of voltage gating of all three HCN isoforms investigated, and allows an interpretation of the different kinetic properties of different isoforms. For example, faster kinetics of HCN1 relative to HCN2/HCN4 are attributable to higher HCN1 voltage sensors' rates and looser voltage-independent interactions between subunits in closed/open transitions. It also accounts for experimental evidence that reduction of sensors' positive charge leads to negative voltage shifts of Po curve, with little change of curve slope. HCN voltage gating thus involves two processes: voltage sensor gating and allosteric opening/closing.