Function of calcium-activated small conductance potassium channel in astrocytes

Ohio State University, Columbus OH

Investigators

Abstract

ABSTRACT Astrocytes express abundant voltage-independent leak-type K+ channels to make the membrane highly permeable to K+ ions and to have a hyperpolarizing membrane potential. These are two requisites for astrocyte function in brain homeostasis. The leak K+ channels generate a characteristic ohmic behavior, commonly called passive, K+ conductance in astrocytes. While the research over the past decades identified several inwardly rectifying K+ channels, such as Kir4.1, to contribute to passive K+ conductance, the molecular identity of a major leak K+ channel, a K+ channel that follows the Goldman-Hodgkin-Katz (GHK) equation to show constant field outward rectification, remains elusive. This proposal aims to solve this longstanding puzzle by examining the functional expression of a small conductance Ca2+-activated K+ channel, SK2 (KCNN2), as a GHK rectifier K+ channel, in astrocytes. Further, this proposal will examine the interaction of SK2 with adrenergic signaling for dynamic regulation of astrocyte passive K+ conductance. The premise underpinning this proposal includes a high expression of SK2 mRNA in freshly dissociated hippocampal astrocytes, the presence of a large portion of passive K+ conductance that is sensitive to a highly selective SK2 inhibitor, apamin, and responsiveness of astrocyte passive K+ conductance to Gq-coupled adrenergic a1 receptor (a1-AR), known to be expressed by astrocytes. These observations compellingly show the SK2 as the long-sought GHK rectifier K+ channel engaged in astrocyte passive K+ conductance. Extending from these preliminary studies, this proposal aims to achieve three specific objectives. First, to correlate the apamin-sensitive passive K+ conductance with the SK2 channel gene (Kcnn2) through inducible astrocytic Kcnn2 knockout (Aldh1l1-Cre/ERT2;Kcnn2fl/fl;Ai9). Second, to validate the observation that Kir4.1 and SK2 work in concert to generate astrocyte passive K+ conductance through inducible Kcnj10/Kcnn2 double gene knockout from astrocytes (Aldh1l1- Cre/ERT2;Kcnn2fl/fl;Kcnj10fl/fl;Ai9). Third, to test a hypothesis that adrenergic signaling modulates K+ passive conductance through the interaction of astrocytic a1-AR and SK2. This project will for the first time correlate SK2 to the long-sought for GHK rectifier K+ channel in astrocyte passive K+ conductance. The results of the interaction of SK2 with adrenergic signaling have the potential to vertically change the “passive” view of astrocyte K+ conductance in brain homeostatic function. Second, through comparative analyses of SK2 and Kir4.1 KO astrocytes, we expect an outcome that would advance the notion that Kir4.1 and SK2 work in concert to implement the K+ uptake and release in the process of [K+]e buffering. Third, the resultant knowledge and validated animal models from this project should facilitate future studies of leak-type SK2 and Kir4.1 in astrocyte physiology and pathology.