Predominant expression of leak-type K⁺ channels provides astrocytes a high membrane permeability to K⁺ ions and a hyperpolarized membrane potential that are crucial for astrocyte function in brain homeostasis. In functionally mature astrocytes, the expression of leak K⁺ channels creates a unique membrane K⁺ conductance that lacks voltage-dependent rectification. Accordingly, the conductance is named ohmic or passive K⁺ conductance. Several inwardly rectifiers and two-pore domain K⁺ channels have been investigated for their contributions to passive conductance. Meanwhile, gap junctional coupling has been postulated to underlie the passive behavior of membrane conductance. It is now clear that the intrinsic properties of K⁺ channels and gap junctional coupling can each act alone or together to bring about a passive behavior of astrocyte conductance. Additionally, while the passive conductance can generally be viewed as a K⁺ conductance, the actual representation of this conductance is a combined expression of multiple known and unknown K⁺ channels, which has been further modified by the intricate morphology of individual astrocytes and syncytial gap junctional coupling. The expression of the inwardly rectifying K⁺ channels explains the inward-going component of passive conductance disobeying Goldman-Hodgkin-Kate (GHK) constant field outward rectification. However, the K⁺ channels encoding the outward-going passive currents remain to be determined in the future. Here, we review our current understanding of ion channels and biophysical mechanisms engaged in the passive astrocyte K⁺ conductance, propose new studies to resolve this long-standing puzzle in astrocyte physiology, and discuss the functional implication(s) of passive behavior of K⁺ conductance on astrocyte physiology.

中文翻译：

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星形胶质细胞钾电导的电无源性

泄漏型 K ^{+通道的主要表达为星形胶质细胞提供了对 K +}离子的高膜通透性和超极化膜电位，这对于星形胶质细胞在脑内稳态中的功能至关重要。在功能成熟的星形胶质细胞中，泄漏 K ⁺通道的表达会产生独特的膜 K ⁺电导，该电导缺乏电压依赖性整流。因此，电导被命名为欧姆或无源K ⁺电导。几个内向整流器和两孔域 K ⁺已经研究了通道对被动电导的贡献。同时，间隙连接耦合被认为是膜电导被动行为的基础。现在很清楚，K ⁺通道和间隙连接耦合的内在特性可以单独或共同作用，从而导致星形胶质细胞电导的被动行为。此外，虽然被动电导通常可以被视为 K ⁺电导，但该电导的实际表示是多个已知和未知 K ⁺通道的组合表达，其已通过单个星形胶质细胞的复杂形态和合胞间隙进一步修改结耦合。向内整流 K ^{+的表达式}通道解释了无源电导的内向分量违反 Goldman-Hodgkin-Kate (GHK) 恒定场外向整流。然而，编码外向无源电流的 K ⁺通道仍有待确定。在这里，我们回顾了我们目前对参与被动星形胶质细胞 K ⁺电导的离子通道和生物物理机制的理解，提出新的研究来解决星形胶质细胞生理学中长期存在的难题，并讨论 K ⁺被动行为的功能意义星形胶质细胞生理学的电导。