Reverse engineering and energetics of high frequency action potential generation

***该提案的重点是了解细胞在具有挑战性和极端情况下的兴奋性，作为一个实验室，以理解生命系统设计的策略，以优化能量和维持内稳态，或动态平衡状态。除了少数例外，细胞电信号是基于一个普遍的原则：控制离子梯度通过膜的耗散，维持低细胞内Na+和细胞外K+浓度。这些梯度为电压尖峰或动作电位（ap）提供驱动力。为了维持兴奋性，离子梯度必须通过（atp燃料）Na+/K+泵的化学作用来恢复，这是一个保持细胞内稳态的过程。这种普遍的操作模式是中枢神经系统中轴突操作的基础，在弱电鱼（如本格曼鱼）中，它产生外部电流，鱼通过这种电流感知环境。在具有挑战性的条件下工作提出了能量学和维持体内平衡的策略问题。*******值得注意的是，在它们的一生中，本征曼原虫不断地产生振荡偶极子样电器官放电（EOD），以固定的个体特定频率起源于电细胞柱。种类范围为200-500Hz。这个器官的1000个左右的非收缩细胞是由通过突触间隙释放的乙酰胆碱驱动的。神经输入确保ap同步发射，产生高度规则的EOD。我们的第一个短期目标是确定这种复杂的高频“设备”如何产生节能的偶极子振荡器。我们的方法是从细胞到整个器官构建EOD，记住，如果要理解EOD，就必须了解离子稳态的细胞物流。与此同时，我的合作者的实验室也在测量排爆装置的信号。到目前为止，低内在排爆变异性很少受到关注，但我们的研究为排爆设计提供了新的见解。大脑输入到EO的信号通过髓鞘轴突提供了一个高频信号，这个信号必须是稳健的。这与我们的第二个短期目标有关，即研究非为此目的而设计的轴突对持续高频放电的反应，包括那些遭受轻度损伤的轴突。我们想了解这些髓鞘神经元是如何恢复兴奋性和稳态的。*******弱电鱼是一个迷人的模型系统，不仅研究能量学，而且研究高频兴奋性的亚细胞和更广泛的水平动力学。对遭受持续异常放电或轻度损伤的轴突的研究将揭示稳态设计的特征。我们的工作以实验为指导，并有几位生物学家的持续投入，确保预测是有根据的，其影响超出了生物物理学领域。*****

***The proposal focuses on understanding cell excitability in challenging and extreme situations as a laboratory to understanding strategies devised by living systems to optimize energetics and maintain homeostasis, or a state of dynamical equilibrium. Cellular electrical signaling is based, with few exceptions, on a universal principle: controlled dissipation of ion gradients across a membrane that sustains low intracellular Na+ and extracellular K+ concentrations. These gradients provide the driving force for voltage spikes, or action potentials (APs). To maintain excitability, ion gradients must be restored by the chemical work of (ATP-fueled) Na+/K+ pumps, a process that preserves cellular homeostasis. This universal mode of operation is the basis of operation for axons in the central nervous system, and, in weakly electric fish such as Eigenmannia, it produces external electric currents by which the fish senses its environment. Operating under challenging conditions raises issues of energetics and strategies to maintain homeostasis.*******Remarkably, throughout their lifetime, Eigenmannia continuously produce an oscillating dipole-like electric organ discharge (EOD) at a fixed individual specific frequency originating from columns of electrocyte cells. The species range is 200-500Hz. The organ's 1000 or so non-contractile cells are driven by releases of acetylcholine through the synaptic gap. The neural input ensures that APs fire synchronously, producing a highly regular EOD. Our first short term goal is to determine how this complex high frequency “device” produces an energy-efficient dipole oscillator. Our approach is to construct EODs from the cell up to the whole organ, remembering that understanding the cellular logistics of ion homeostasis is mandatory if the EOD is to be understood. In parallel, measurements of the EOD signal are being carried out in my collaborator's lab. The low intrinsic EOD variability has received little attention so far, but our examination promises fresh insights into EO design. The brain's input into the EO provides a high frequency signal via myelinated axons which must be robust. This connects to our second short term goal, investigating the response to sustained high frequency firing in axons not designed for that purpose, including those that have suffered mild damage. We want to understand how these myelinated neurons recover excitability and homeostasis.*******The weakly electric fish is a fascinating model system for studying not only the energetics but the subcellular and broader level dynamics of high frequency excitability. The study of axons subjected to sustained abnormal firing or mildly damaged will reveal homeostatic design features. Our work guided by experiment and with continuous input from several biologists ensures that the predictions are well grounded and their impact extends beyond the realms of biophysics.*****