Long-lasting dephosphorylation of connexin 43 in acute seizures is regulated by NMDA receptors in the rat cerebral cortex

Abstract

Abstract. Gap junctions consisting of connexin 43 subunits provide intercellular communication between astrocytes, contributing to their function of maintaining the central nervous system (CNS) microenvironment. Magnetic resonance imaging (MRI) studies demonstrate prolonged astrocyte swelling related to seizures, while in vitro studies show the disruption of intercellular coupling and the cytotoxic swelling of astrocytes in seizure-equivalent environments. We examined the relation between astrocyte swelling and connexin 43 regulation using an in vivo seizure model. Generalised tonic-clonic convulsions were induced in adult rats using intraperitoneally (i.p.)-administered 4-aminopyridine (4-AP). The expression of connexin 43 mRNA and protein at 1, 3 and 24 h after seizure induction was measured. Astrocytic swelling was assessed at the same time points using transmission electron microscopy. mRNA and protein levels remained unaltered at all time periods. However, a significant (~50%) reduction was found in the amount of phosphorylated (P1, P2) to unphosphorylated (NP) forms of connexin 43 at 3 h. The amount increased thereafter, but was still significantly lower than in the controls at 24 h postseizure. Simultaneously, marked astrocytic swelling was measured in the neocortex. Pre-treatment with N-methyl-Daspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) resulted in the amelioration of seizure symptoms and the prevention of connexin 43 dephosphorylation, as well as significantly reduced astrocytic swelling. Dephosphorylation of connexin 43 was shown to reduce astrocytic gap junction (GJ) permeability. Our results therefore suggest that, during acute seizures, a prolonged inhibition of intercellular coupling develops in the astrocyte network. This accounts for the longlasting astrocyte swelling observed, and potentially impairs buffering function. The results also imply that this uncoupling is regulated through neuronal and/or glial NMDA-type glutamate receptors.

Activation of nicotinamide adenine dinucleotide phosphate oxidase is the primary trigger of epileptic seizures in rodent models

“…NOX-induced oxidative stress transiently inhibits Na/K-ATPase, 36 restricting the uptake of extracellular K + (increased by several mM at the very beginning of seizure initiation 19 ) as well as the efflux of intracellular Na + , thus giving rise to focal network depolarization. In addition, we observed significant tissue (astrocytic) swelling coincident at seizure onset with the sentinel spike (see Fig 8A; see also Zador et al 38 ) that can augment the extracellular K + /glutamate concentrations even further by reducing extracellular volume. In addition, we observed significant tissue (astrocytic) swelling coincident at seizure onset with the sentinel spike (see Fig 8A; see also Zador et al 38 ) that can augment the extracellular K + /glutamate concentrations even further by reducing extracellular volume.…”

Suppression of PKCε-mediated mitochondrial connexin 43 phosphorylation at serine 368 is involved in myocardial mitochondrial dysfunction in a rat model of dilated cardiomyopathy

“…Similar to Cx43, PKCε is also located in the mitochondria, which suggests a possible interaction between Cx43 and PKCε in the mitochondria (18). Increasing evidence indicates that the phosphorylation status of Cx43 is not static, but fluctuates in response to cell stress (19)(20)(21)(22). In the present study, decreased protein expression of PKCε was observed in the myocardial and mitochondrial protein extracts of the DCM rats, and the PKCε activities also decreased by ~60%.…”

Blockade of Astrocytic Glutamate Uptake in the Prefrontal Cortex Induces Anhedonia

“…Chronic unpredictable stressFa preclinical model that induces depressive-like symptoms in animalsFhas been shown to induce astrocytic gap junction dysfunction and consequent decreases in connexin 43, an astrocytespecific gap junction protein, in the PFC of rats (Sun et al, 2012). The effects of these manipulations have been shown both in vitro and in vivo to be glutamate dependent (Ozog et al, 2002;Zador et al, 2008). These results suggest that depressive-like outcomes correlate with increases in glutamate and astrocyte dysregulation that may lead to increases in glutamate-changes that, therefore, probably contribute to an anhedonic phenotype.…”