Dissipation of transmembrane potassium gradient is the main cause of cerebral ischemia-induced depolarization in astrocytes and neurons

Abstract

Membrane potential (V) depolarization occurs immediately following cerebral ischemia and is devastating for the astrocyte homeostasis and neuronal signaling. Previously, an excessive release of extracellular K and glutamate has been shown to underlie an ischemia-induced V depolarization. Ischemic insults should impair membrane ion channels and disrupt the physiological ion gradients. However, their respective contribution to ischemia-induced neuronal and glial depolarization and loss of neuronal excitability are unanswered questions. A short-term oxygen-glucose deprivation (OGD) was used for the purpose of examining the acute effect of ischemic conditions on ion channel activity and physiological K gradient in neurons and glial cells. We show that a 30 min OGD treatment exerted no measurable damage to the function of membrane ion channels in neurons, astrocytes, and NG2 glia. As a result of the resilience of membrane ion channels, neuronal spikes last twice as long as our previously reported 15 min time window. In the electrophysiological analysis, a 30 min OGD-induced dissipation of transmembrane K gradient contributed differently in brain cell depolarization: severe in astrocytes and neurons, and undetectable in NG2 glia. The discrete cellular responses to OGD corresponded to a total loss of 69% of the intracellular K contents in hippocampal slices as measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). A major brain cell depolarization mechanism identified here is important for our understanding of cerebral ischemia pathology. Additionally, further understanding of the resilient response of NG2 glia to ischemia-induced intracellular K loss and depolarization should facilitate the development of future stroke therapy.

Epileptiform Neuronal Discharges Impair Astrocyte Syncytial Isopotentiality in Acute Hippocampal Slices

“…In voltage-clamp recording, the depolarization steps induced a sequential activation of voltage-gated inward Na + (IN a ), outward transient K + channels (IK a ) and delayed rectifying K + channels (IK d ) ( Figure 1B). These properties were consistent with our previous reports [29,31,32].…”

“…To prepare freshly dissociated astrocytes, hippocampal brain slices were first incubated for 30 min in oxygenated aCSF supplemented with 0.6 µM SR101 at 34 • C. Then, the CA1 regions were dissected out and cut into~1 mm 3 pieces and transferred into a 1.5 mL Eppendorf tube containing oxygenated aCSF supplemented with 24 U/mL papain and 0.8 mg/mL L-cysteine for 7 min at RT. After papain digestion, the tissues were gently triturated 5-7 times into a cell suspension, which was then transferred into the recording chamber [28,29]. Although the cell suspensions contain tissue blocks varying in the number of astrocytes, only single dissociated astrocytes were used in this study.…”

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

“…This sequence of events is called the ischemic pathway, which begins with energy depletion and glutamate excitotoxicity, and ends in cell death (Lai et al, 2014;Cuartero et al, 2016; Figure 1). According to the changes in membrane potential, the most vulnerable cells to 30-min OGD are neurons, followed by astrocytes, while NG2 glia showed no significant pathological alterations (Du et al, 2018). Moreover, microglial cells are least vulnerable to ischemia because they express glutamate receptors only after the onset of pathological conditions when they become reactive (Gottlieb and Matute, 1997).…”

Syncytial isopotentiality: A system‐wide electrical feature of astrocytic networks in the brain

“…Then, the CA1 region was dissected out and cut into ~1 mm 3 pieces and transferred into a 1.5 ml Eppendorf tube containing oxygenated aCSF supplemented with 24 U/ml papain and 0.8 mg/ml l ‐cysteine for 7 min at RT. After papain digestion, the tissues were gently triturated 5–7 times into a cell suspension, which is then transferred into the recording chamber (Du et al, , ).…”