Potassium buffering by M�ller cells isolated from the center and periphery of the frog retina

Skatchkov, Serguei N.; Krůšek, Jan; Reichenbach, Andreas; Orkand, R.K.

doi:10.1002/(sici)1098-1136(199908)27:2<171::aid-glia7>3.0.co;2-f

Cited by 26 publications

(6 citation statements)

References 31 publications

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“…One of the major functions of astrocytes is the removal of excess potassium from active synaptic areas [11,18]. Kir4.1 channels in astrocytes contribute to potassium uptake, therefore, we tested the potassium uptake capabilities of astrocytes via Kir channels using a physiologically relevant protocol [12,14,19,26]. We clamped each astrocyte to their native resting membrane potential, thus zero current, while perfusing the slice with control ACSF containing 2.5 mM K + .…”

Section: Resultsmentioning

confidence: 99%

“…Using whole-cell voltage-clamp to record from astrocytes in stratum radiatum area of hippocampal slices from db/db diabetic and db/+ control mice, we measured inward K + current in response to switching the external solution from one containing 2.5 mM K + to one containing 10 mM K + in the presence and absence of 100 µM Ba 2+ [14,19]. Kir-dependent inward currents were obtained by subtracting the inward current in the presence of barium from the current in the absence of barium.…”

Section: Selection and Recording From Astrocytesmentioning

confidence: 99%

“…Astrocytes have a hyperpolarized membrane potential mainly due to the expression of inwardly rectifying potassium channels 4.1 (Kir4.1) that provide the major K + conductance [11][12][13]16,17]. These channels play a fundamental role in buffering excess K + released after neuronal activity and contribute to removal of excess glutamate by processes called potassium buffering and glutamate clearance, respectively [12][13][14]18,19].…”

Section: Introductionmentioning

confidence: 99%

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Downregulation of Astrocytic Kir4.1 Potassium Channels Is Associated with Hippocampal Neuronal Hyperexcitability in Type 2 Diabetic Mice

et al. 2020

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Epilepsy, characterized by recurrent seizures, affects 1% of the general population. Interestingly, 25% of diabetics develop seizures with a yet unknown mechanism. Hyperglycemia downregulates inwardly rectifying potassium channel 4.1 (Kir4.1) in cultured astrocytes. Therefore, the present study aims to determine if downregulation of functional astrocytic Kir4.1 channels occurs in brains of type 2 diabetic mice and could influence hippocampal neuronal hyperexcitability. Using whole-cell patch clamp recording in hippocampal brain slices from male mice, we determined the electrophysiological properties of stratum radiatum astrocytes and CA1 pyramidal neurons. In diabetic mice, astrocytic Kir4.1 channels were functionally downregulated as evidenced by multiple characteristics including depolarized membrane potential, reduced barium-sensitive Kir currents and impaired potassium uptake capabilities of hippocampal astrocytes. Furthermore, CA1 pyramidal neurons from diabetic mice displayed increased spontaneous activity: action potential frequency was ≈9 times higher in diabetic compared with non-diabetic mice and small EPSC event frequency was significantly higher in CA1 pyramidal cells of diabetics compared to non-diabetics. These differences were apparent in control conditions and largely pronounced in response to the pro-convulsant 4-aminopyridine. Our data suggest that astrocytic dysfunction due to downregulation of Kir4.1 channels may increase seizure susceptibility by impairing astrocytic ability to maintain proper extracellular homeostasis.

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Section: Resultsmentioning

confidence: 99%

Section: Selection and Recording From Astrocytesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Downregulation of Astrocytic Kir4.1 Potassium Channels Is Associated with Hippocampal Neuronal Hyperexcitability in Type 2 Diabetic Mice

et al. 2020

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“…We used a physiologically relevant protocol to test the ability of astrocytes to buffer potassium by measuring membrane currents elicited in response to an extracellular K + step (Skatchkov et al, 1995, Skatchkov et al, 1999, Zhou et al, 2000, Kucheryavykh et al, 2007, Inyushin et al, 2010). Whole cell patch clamp recordings were done at holding potential equal to the cell membrane potential (−61.6 mV ± 2.0 SEM for control glucose and −60.6 mV ± 2.8 SEM for high glucose) with constant whole cell bath perfusion.…”

Section: 0 Resultsmentioning

confidence: 99%

Hyperglycemia reduces functional expression of astrocytic Kir4.1 channels and glial glutamate uptake

et al. 2015

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Diabetics are at risk for a number of serious health complications including an increased incidence of epilepsy and poorer recovery after ischemic stroke. Astrocytes play a critical role in protecting neurons by maintaining extracellular homeostasis and preventing neurotoxicity through glutamate uptake and potassium buffering. These functions are aided by the presence of potassium channels, such as Kir4.1 inwardly rectifying potassium channels, in the membranes of astrocytic glial cells. The purpose of the present study was to determine if hyperglycemia alters Kir4.1 potassium channel expression and homeostatic functions of astrocytes. We used q-PCR, Western blot, patch-clamp electrophysiology studying voltage and potassium step responses and a colorimetric glutamate clearance assay to assess Kir4.1 channel levels and homeostatic functions of astrocytes grown in normal and high glucose conditions. We found that astrocytes grown in high glucose (25 mM) had an approximately 50% reduction in Kir4.1 mRNA and protein expression as compared with those grown in normal glucose (5 mM). These reductions occurred within 4 to 7 days of exposure to hyperglycemia, whereas reversal occurred between 7 to 14 days after return to normal glucose. The decrease in functional Kir channels in the astrocytic membrane was confirmed using barium to block Kir channels. In the presence of 100 μm barium, the currents recorded from astrocytes in response to voltage steps were reduced by 45%. Furthermore, inward currents induced by stepping extracellular [K+]o from 3 to 10 mM (reflecting potassium uptake) were 50% reduced in astrocytes grown in high glucose. In addition, glutamate clearance by astrocytes grown in high glucose was significantly impaired. Taken together, our results suggest that down-regulation of astrocytic Kir4.1 channels by elevated glucose may contribute to the underlying pathophysiology of diabetes-induced CNS disorders and contribute to the poor prognosis after stroke.

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“…Test solutions were applied without interruption using as a baseline physiological 3mM [K + ]. Solutions with decreased extracellular [K + ] 1mM for outward current or increased [K + ] to 10mM for inward current within the physiological range were applied (Skatchkov et al, 1999). In these experiments we used a voltage step protocol as previously described (Skatchkov et al, 2006; Kucheryavykh et al, 2007; 2008; Inyushin et al, 2010).…”

Section: Methodsmentioning

confidence: 99%

A-Kinase-Anchoring Protein (AKAP150) is expressed in Astrocytes and Upregulated in Response to Ischemia

et al. 2018

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A-kinase-anchoring proteins, AKAPs, are scaffolding proteins that associate with kinases and phosphatases, and direct them to a specific submembrane site to coordinate signaling events. AKAP150, a rodent ortholog of human AKAP79, has been extensively studied in neurons, but very little is known about the localization and function of AKAP150 in astrocytes, the major cell type in brain. Thus, in this study, we assessed the localization of AKAP150 in astrocytes and elucidated its role during physiological and ischemic conditions. Herein, we demonstrate that AKAP150 is localized in astrocytes and is up-regulated during ischemia both in vitro and in vivo. Knock-down of AKAP150 by RNAi depolarizes the astrocytic membrane potential and substantially reduces by 80% the ability of astrocytes to take up extracellular potassium during ischemic conditions. Therefore, upregulation of AKAP150 during ischemia preserves potassium conductance and the associated hyperpolarized membrane potential of astrocytes; properties of astrocytes needed to maintain extracellular brain homeostasis. Taken together, these data suggest that AKAP150 may play a pivotal role in the neuroprotective mechanism of astrocytes during pathological conditions.

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Potassium buffering by M�ller cells isolated from the center and periphery of the frog retina

Cited by 26 publications

References 31 publications

Downregulation of Astrocytic Kir4.1 Potassium Channels Is Associated with Hippocampal Neuronal Hyperexcitability in Type 2 Diabetic Mice

Downregulation of Astrocytic Kir4.1 Potassium Channels Is Associated with Hippocampal Neuronal Hyperexcitability in Type 2 Diabetic Mice

Hyperglycemia reduces functional expression of astrocytic Kir4.1 channels and glial glutamate uptake

A-Kinase-Anchoring Protein (AKAP150) is expressed in Astrocytes and Upregulated in Response to Ischemia

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