Bartos Daniel C, Morotti Stefano, Ginsburg Kenneth S, Grandi Eleonora, Bers Donald M
Department of Pharmacology, University of California, Davis, Davis, CA 95616, USA.
J Physiol. 2017 Apr 1;595(7):2253-2268. doi: 10.1113/JP273676. Epub 2017 Mar 28.
[Ca ] enhanced rabbit ventricular slowly activating delayed rectifier K current (I ) by negatively shifting the voltage dependence of activation and slowing deactivation, similar to perfusion of isoproterenol. Rabbit ventricular rapidly activating delayed rectifier K current (I ) amplitude and voltage dependence were unaffected by high [Ca ] . When measuring or simulating I during an action potential, I was not different during a physiological Ca transient or when [Ca ] was buffered to 500 nm.
The slowly activating delayed rectifier K current (I ) contributes to repolarization of the cardiac action potential (AP). Intracellular Ca ([Ca ] ) and β-adrenergic receptor (β-AR) stimulation modulate I amplitude and kinetics, but details of these important I regulators and their interaction are limited. We assessed the [Ca ] dependence of I in steady-state conditions and with dynamically changing membrane potential and [Ca ] during an AP. I was recorded from freshly isolated rabbit ventricular myocytes using whole-cell patch clamp. With intracellular pipette solutions that controlled free [Ca ] , we found that raising [Ca ] from 100 to 600 nm produced similar increases in I as did β-AR activation, and the effects appeared additive. Both β-AR activation and high [Ca ] increased maximally activated tail I , negatively shifted the voltage dependence of activation, and slowed deactivation kinetics. These data informed changes in our well-established mathematical model of the rabbit myocyte. In both AP-clamp experiments and simulations, I recorded during a normal physiological Ca transient was similar to I measured with [Ca ] clamped at 500-600 nm. Thus, our study provides novel quantitative data as to how physiological [Ca ] regulates I amplitude and kinetics during the normal rabbit AP. Our results suggest that micromolar [Ca ] , in the submembrane or junctional cleft space, is not required to maximize [Ca ] -dependent I activation during normal Ca transients.
[Ca]通过使激活的电压依赖性负向移位和减慢失活来增强兔心室缓慢激活延迟整流钾电流（I），类似于异丙肾上腺素灌注。兔心室快速激活延迟整流钾电流（I）的幅度和电压依赖性不受高[Ca]的影响。在动作电位期间测量或模拟I时，在生理性Ca瞬变期间或[Ca]缓冲至500 nM时，I没有差异。
缓慢激活延迟整流钾电流（I）有助于心脏动作电位（AP）的复极化。细胞内Ca（[Ca]）和β-肾上腺素能受体（β-AR）刺激调节I的幅度和动力学，但这些重要的I调节剂及其相互作用的细节有限。我们评估了在稳态条件下以及在AP期间膜电位和[Ca]动态变化时I对[Ca]的依赖性。使用全细胞膜片钳从新鲜分离的兔心室肌细胞记录I。通过控制游离[Ca]的细胞内移液管溶液，我们发现将[Ca]从100 nM提高到600 nM产生的I增加与β-AR激活相似，并且这些作用似乎是相加的。β-AR激活和高[Ca]均增加了最大激活尾电流I，使激活的电压依赖性负向移位，并减慢了失活动力学。这些数据为我们完善的兔心肌细胞数学模型带来了变化。在AP钳实验和模拟中，在正常生理性Ca瞬变期间记录的I与在[Ca]钳制在500 - 600 nM时测量的I相似。因此，我们的研究提供了关于生理性[Ca]如何在正常兔AP期间调节I幅度和动力学的新定量数据。我们的结果表明，在正常Ca瞬变期间，不需要微摩尔浓度的[Ca]来使依赖于[Ca]的I激活最大化，在亚膜或连接间隙空间中也是如此。
