Opening of Astrocytic Mitochondrial ATP-Sensitive Potassium Channels Upregulates Electrical Coupling between Hippocampal Astrocytes in Rat Brain Slices

Abstract

Astrocytes form extensive intercellular networks through gap junctions to support both biochemical and electrical coupling between adjacent cells. ATP-sensitive K+ (KATP) channels couple cell metabolic state to membrane excitability and are enriched in glial cells. Activation of astrocytic mitochondrial KATP (mitoKATP) channel regulates certain astrocytic functions. However, less is known about its impact on electrical coupling between directly coupled astrocytes ex vivo. By using dual patch clamp recording, we found that activation of mitoKATP channel increased the electrical coupling ratio in brain slices. The electrical coupling ratio started to increase 3 min after exposure to Diazoxide, a mitoKATP channel activator, peaked at 5 min, and maintained its level with little adaptation until the end of the 10-min treatment. Blocking the mitoKATP channel with 5-hydroxydecanoate, inhibited electrical coupling immediately, and by 10-min, the ratio dropped by 71% of the initial level. Activation of mitoKATP channel also decreased the latency time of the transjunctional currents by 50%. The increase in the coupling ratio resulting from the activation of the mitoKATP channel in a single astrocyte was further potentiated by the concurrent inhibiting of the channel on the recipient astrocyte. Furthermore, Meclofenamic acid, a gap-junction inhibitor which completely blocked the tracer coupling, hardly reversed the impact of mitoKATP channel's activation on electrical coupling (by 7%). The level of mitochondrial Connexin43, a gap junctional subunit, significantly increased by 70% in astrocytes after 10-min Diazoxide treatment. Phospho-ERK signals were detected in Connexin43 immunoprecipitates in the Diazoxide-treated astrocytes, but not untreated control samples. Finally, inhibiting ERK could attenuate the effects of Diazoxide on electrical coupling by 61%. These findings demonstrate that activation of astrocytic mitoKATP channel upregulates electrical coupling between hippocampal astrocytes ex vivo. In addition, this effect is mainly via up-regulation of the Connexin43-constituted gap junction coupling by an ERK-dependent mechanism in the mitochondria.

KATP Channel Opener Diazoxide Prevents Neurodegeneration: A New Mechanism of Action via Antioxidative Pathway Activation

“…For instance, the activation of Nrf2 nuclear translocation has been described as the main mechanism of action involved in the beneficial effect of fumaric esters for the treatment of MS [33]. Nrf2 mediates the activation of detoxifying phase II enzymes via mitochondrial oxidative stress signaling [34], [35] where mito-K ATP channels function play a crucial role [36]. This pathway may thus play a critical role for cellular protection in an environment of oxidative stress and may represent an interesting therapeutic target in neurodegenerative diseases.…”

Mechanism of Mitochondrial Connexin43′s Protection of the Neurovascular Unit under Acute Cerebral Ischemia-Reperfusion Injury

“…Thus, in this study, we chose DZX at concentrations of 20 mmol/L and 5-HD at concentrations of 100 mmol/L to interfere with the control of mitoKATP channel activation. Wang et al suggested that the opening of astrocytic mitoKATP channels resulted in increased permeability of the mitochondrial GJs for K + influx into the soma and increased electrical coupling [ 32 ]. Meanwhile, we found that the brain infarction volume, apoptosis rate, and mitochondrial structure and function were improved by DZX following I/R injury, which was reversed by 5-HD.…”

Opening of KATP Channel Regulates Tonic Currents From Pyramidal Neurons in Rat Brain

“…Previous studies have suggested that DIZ can prevent the initial hyperexcitability produced by anoxia, 21 while according to our previous research we deduced that the anticonvulsant action of mitoK ATP channels is achieved, at least in part, by enhancing astrocytic mitoK ATP channel-regulated gap-junction coupling 22 and electrical coupling 19 between astrocytes, in addition to neuronal mitoK ATP channel-modulated excitability. The present study revealed a novel pharmacological profile of mitoK ATP channel activators as regulators of tonic GABA transmission, and our results may provide a new strategy for antiepileptic treatments.…”