TY - JOUR

T1 - Glutamate transporter-associated anion channels adjust intracellular chloride concentrations during glial maturation

AU - Untiet, Verena

AU - Kovermann, Peter

AU - Gerkau, Niklas J

AU - Gensch, Thomas

AU - Rose, Christine R

AU - Fahlke, Christoph

N1 - © 2016 Wiley Periodicals, Inc.

PY - 2017

Y1 - 2017

N2 - Astrocytic volume regulation and neurotransmitter uptake are critically dependent on the intracellular anion concentration, but little is known about the mechanisms controlling internal anion homeostasis in these cells. Here we used fluorescence lifetime imaging microscopy (FLIM) with the chloride-sensitive dye MQAE to measure intracellular chloride concentrations in murine Bergmann glial cells in acute cerebellar slices. We found Bergmann glial [Cl- ]int to be controlled by two opposing transport processes: chloride is actively accumulated by the Na+ -K+ -2Cl- cotransporter NKCC1, and chloride efflux through anion channels associated with excitatory amino acid transporters (EAATs) reduces [Cl- ]int to values that vary upon changes in expression levels or activity of these channels. EAATs transiently form anion-selective channels during glutamate transport, and thus represent a class of ligand-gated anion channels. Age-dependent upregulation of EAATs results in a developmental chloride switch from high internal chloride concentrations (51.6 ± 2.2 mM, mean ± 95% confidence interval) during early development to adult levels (35.3 ± 0.3 mM). Simultaneous blockade of EAAT1/GLAST and EAAT2/GLT-1 increased [Cl- ]int in adult glia to neonatal values. Moreover, EAAT activation by synaptic stimulations rapidly decreased [Cl- ]int . Other tested chloride channels or chloride transporters do not contribute to [Cl- ]int under our experimental conditions. Neither genetic removal of ClC-2 nor pharmacological block of K+ -Cl- cotransporter change resting Bergmann glial [Cl- ]int in acute cerebellar slices. We conclude that EAAT anion channels play an important and unexpected role in adjusting glial intracellular anion concentration during maturation and in response to cerebellar activity. GLIA 2017;65:388-400.

AB - Astrocytic volume regulation and neurotransmitter uptake are critically dependent on the intracellular anion concentration, but little is known about the mechanisms controlling internal anion homeostasis in these cells. Here we used fluorescence lifetime imaging microscopy (FLIM) with the chloride-sensitive dye MQAE to measure intracellular chloride concentrations in murine Bergmann glial cells in acute cerebellar slices. We found Bergmann glial [Cl- ]int to be controlled by two opposing transport processes: chloride is actively accumulated by the Na+ -K+ -2Cl- cotransporter NKCC1, and chloride efflux through anion channels associated with excitatory amino acid transporters (EAATs) reduces [Cl- ]int to values that vary upon changes in expression levels or activity of these channels. EAATs transiently form anion-selective channels during glutamate transport, and thus represent a class of ligand-gated anion channels. Age-dependent upregulation of EAATs results in a developmental chloride switch from high internal chloride concentrations (51.6 ± 2.2 mM, mean ± 95% confidence interval) during early development to adult levels (35.3 ± 0.3 mM). Simultaneous blockade of EAAT1/GLAST and EAAT2/GLT-1 increased [Cl- ]int in adult glia to neonatal values. Moreover, EAAT activation by synaptic stimulations rapidly decreased [Cl- ]int . Other tested chloride channels or chloride transporters do not contribute to [Cl- ]int under our experimental conditions. Neither genetic removal of ClC-2 nor pharmacological block of K+ -Cl- cotransporter change resting Bergmann glial [Cl- ]int in acute cerebellar slices. We conclude that EAAT anion channels play an important and unexpected role in adjusting glial intracellular anion concentration during maturation and in response to cerebellar activity. GLIA 2017;65:388-400.

KW - Acetates/pharmacology

KW - Age Factors

KW - Animals

KW - Animals, Newborn

KW - Aspartic Acid/pharmacology

KW - Benzopyrans/pharmacology

KW - Bumetanide/pharmacology

KW - Cerebellum/cytology

KW - Chlorides/metabolism

KW - Excitatory Amino Acid Transporter 1/antagonists & inhibitors

KW - Gene Expression Regulation, Developmental/drug effects

KW - Glial Fibrillary Acidic Protein/genetics

KW - Indenes/pharmacology

KW - Intracellular Fluid/drug effects

KW - Mice

KW - Mice, Transgenic

KW - Nerve Net/physiology

KW - Neuroglia/cytology

KW - Sodium Potassium Chloride Symporter Inhibitors/pharmacology

KW - Solute Carrier Family 12, Member 2/metabolism

KW - Voltage-Dependent Anion Channels/metabolism

U2 - 10.1002/glia.23098

DO - 10.1002/glia.23098

M3 - Journal article

C2 - 27859594

VL - 65

SP - 388

EP - 400

JO - GLIA

JF - GLIA

SN - 0894-1491

IS - 2

ER -