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，以了解生命系统设计的策略，以优化能量和维持稳态，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：控制跨膜离子梯度的耗散，维持低的细胞内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+泵的化学工作来恢复，这是一个保持细胞内稳态的过程。这种普遍的运作模式是中枢神经系统轴突运作的基础，在弱电鱼类（如Eigenmannia）中，它产生外部电流，使鱼类感知其环境。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，在它们的整个生命周期中，Eigenmannia连续产生振荡的偶极样电器官放电（EOD），其频率是固定的个体特定频率，来源于电细胞柱。频率范围为200- 500 Hz。该器官的大约1000个非收缩性细胞由通过突触间隙释放的乙酰胆碱驱动。神经输入确保AP同步发射，产生高度规则的爆炸物处理。我们的第一个短期目标是确定这个复杂的高频“设备”如何产生节能的偶极振荡器。我们的方法是构建从细胞到整个器官的EOD，记住，如果要理解EOD，理解离子稳态的细胞物流是必需的。与此同时，我的合作者的实验室正在对爆炸物处理信号进行测量。到目前为止，低的固有EOD可变性很少受到关注，但我们的检查承诺EO设计的新见解。大脑对EO的输入通过有髓轴突提供高频信号，这必须是鲁棒的。这与我们的第二个短期目标有关，即研究轴突对持续高频放电的反应，这些轴突不是为该目的而设计的，包括那些遭受轻度损伤的轴突。我们想了解这些有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，但亚细胞和更广泛的水平动态的高频兴奋性。对受到持续异常放电或轻度损伤的轴突的研究将揭示稳态设计特征。我们的工作以实验为指导，并得到几位生物学家的持续投入，确保预测有充分的依据，其影响超出了生物物理学的领域。

***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.*****