Kv2.1 expression in giant reticular neurons of the postnatal mouse brain

Previous experiments charted the development of behavioral arousal in postnatal mice. From Postnatal Day 3 (P3) to Postnatal Day 6 (P6) mice (a) become significantly more active, "arousable"; and (b) in large reticular neurons, nucleus gigantocellularis (NGC), patch clamp recordings reveal a significantly increased ability to fire high frequency trains of action potentials as are associated with elevated cortical arousal. These action potential trains depend on delayed rectifiers such as Kv2.1. Here we report tracking the development of expression of a delayed rectifier, Kv2.1 in NGC neurons crucial for initiating CNS arousal. In tissue sections, light microscope immunohistochemistry revealed that expression of Kv2.1 in NGC neurons is greater at day P6 than at P3. Electron microscope immunohistochemistry revealed Kv2.1 labeling on the plasmalemmal surface of soma and dendrites, greater on P6 than P3. In brainstem reticular neuron cell culture, Kv2.1 immunocytochemistry increased monotonically from Days-In-Vitro 3-10, paralleling the ability of such neurons to fire action potential trains. The increase of Kv2.1 expression from P3 to P6, perhaps in conjunction with other delayed rectifier currents, could permit the ability to fire action potential trains in NGC neurons. Further work with genetically identified NGC neurons is indicated.

MicroRNA-1 accelerates the shortening of atrial effective refractory period by regulating KCNE1 and KCNB2 expression: an atrial tachypacing rabbit model

Background

The potential mechanisms of microRNA-1 (miR-1) in the electrical remodeling of atrial fibrillation remain unclear. The purpose of this study was to evaluate the effects of miR-1 on the atrial effective refractory period (AERP) in a right atrial tachypacing model and to elucidate the potential mechanisms.

Methods and Results

QRT-PCR and western blot were used to detect the expression of the miR-1, KCNE1, and KCNB2 genes after 1-week of right atrial tachypacing in New Zealand white rabbits. The AERP was measured using a programmable multichannel stimulator, and atrial fibrillation was induced by burst stimulation invivo. The slowly activating delayed rectifier potassium current (IKs) and AERP in atrial cells were measured by whole cell patch clamp invitro. Right atrial tachypacing upregulated miR-1 expression and downregulated KCNE1 and KCNB2 in this study, while the AERP was decreased and the atrial IKs increased. The downregulation of KCNE1 and KCNB2 levels was greater when miR-1 was further upregulated through invivo lentiviral infection. Electrophysiological tests indicated a shorter AERP, a great increase in the IKs and a higher atrial fibrillation inducibility. In addition, similar results were found when the levels of KCNE1 and KCNB2 were downregulated by smallinterferingRNA while keeping miR-1 level unaltered. Conversely, knockdown of miR-1 by anti-miR-1 inhibitor oligonucleotides alleviated the downregulation of KCNE1 and KCNB2, the shortening of AERP, and the increase in the IKs. KCNE1 and KCNB2 as the target genes for miR-1 were confirmed by luciferase activity assay.

Conclusions

These results indicate that miR-1 accelerates right atrial tachypacing-induced AERP shortening by targeting potassium channel genes, which further suggests that miR-1 plays an important role in the electrical remodeling of atrial fibrillation and exhibits significant clinical relevance as a potential therapeutic target for atrial fibrillation.

Hepatitis C virus NS5A inhibits mixed lineage kinase 3 to block apoptosis

Hepatitis C virus (HCV) infection results in the activation of numerous stress responses including oxidative stress, with the potential to induce an apoptotic state. Previously we have shown that HCV attenuates the stress-induced, p38MAPK-mediated up-regulation of the K(+) channel Kv2.1, to maintain the survival of infected cells in the face of cellular stress. We demonstrated that this effect was mediated by HCV non-structural 5A (NS5A) protein, which impaired p38MAPK activity through a polyproline motif-dependent interaction, resulting in reduction of phosphorylation activation of Kv2.1. In this study, we investigated the host cell proteins targeted by NS5A to mediate Kv2.1 inhibition. We screened a phage-display library expressing the entire complement of human SH3 domains for novel NS5A-host cell interactions. This analysis identified mixed lineage kinase 3 (MLK3) as a putative NS5A interacting partner. MLK3 is a serine/threonine protein kinase that is a member of the MAPK kinase kinase (MAP3K) family and activates p38MAPK. An NS5A-MLK3 interaction was confirmed by co-immunoprecipitation and Western blot analysis. We further demonstrate a novel role of MLK3 in the modulation of Kv2.1 activity, whereby MLK3 overexpression leads to the up-regulation of channel activity. Accordingly, coexpression of NS5A suppressed this stimulation. Additionally we demonstrate that overexpression of MLK3 induced apoptosis, which was also counteracted by NS5A. We conclude that NS5A targets MLK3 with multiple downstream consequences for both apoptosis and K(+) homeostasis.

Apoptotic surface delivery of K+ channels

Apoptosis in cortical neurons requires efflux of cytoplasmic potassium mediated by a surge in Kv2.1 channel activity. Pharmacological blockade or molecular disruption of these channels in neurons prevents apoptotic cell death, while ectopic expression of Kv2.1 channels promotes apoptosis in non-neuronal cells. Here, we use a cysteine-containing mutant of Kv2.1 and a thiol-reactive covalent inhibitor to demonstrate that the increase in K+ current during apoptosis is due to de novo insertion of functional channels into the plasma membrane. Biotinylation experiments confirmed the delivery of additional Kv2.1 protein to the cell surface following an apoptotic stimulus. Finally, expression of botulinum neurotoxins that cleave syntaxin and synaptosome-associated protein of 25 kDa (SNAP-25) blocked upregulation of surface Kv2.1 channels in cortical neurons, suggesting that target soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins support proapoptotic delivery of K+ channels. These data indicate that trafficking of Kv2.1 channels to the plasma membrane causes the apoptotic surge in K+ current.

[The role of subtypes of voltage-gated K+ channels in pulmonary vasoconstriction induced by 15-hydroeicosatetraenoic acid]

AIM

To observe the effect of subtypes of Kv channels in rat pulmonary artery smooth muscle cells (PASMCs) on the process of pulmonary vasoconstriction induced by 15-HETE.

METHODS

In the present study, ring of rabbit PA with specific Kv channel blockers were employed to functionally identify certain channel subtypes that took part in the process of 15-HETE induced pulmonary vasoconstriction; RT-PCR and Western blotting analysis were also used to measure the expression of subtypes of Kv in PASMCs exposed to 15-HETE,chronic hypoxia.

RESULTS

Blocking of Kv1. 1, Kv1. 2, Kv1. 3 and Kv1. 6 channels did not affect 15-HETE induced vasoconstriction in normoxic rats; 15-HETE did not affect expression of Kv1. 1 and Kv1. 2 channels; 15-HETE significantly downregulated the expression of mRNA and protein of Kv1. 5 and Kv2. 1 in rat PASMCs.

CONCLUSION

The results suggested that hypoxia may block Kv1. 5 and Kv2. 1 channels via 15-HETE mediated mechanism, leading to decrease numbers of functional Kv1. 5 and Kv2. 1 channels in PASMCs, leading to PA vasoconstriction.

[mRNA expression of voltage-dependent potassium channels in the brain of rats after middle cerebral artery occlusion]

AIM

To study the mRNA expression changes in the brain of rats after middle cerebral artery occlusion.

METHODS

Middle cerebral artery occlusion was used to induce ischemia in rat brain. The mRNA expression of voltage-dependent potassium channel subtypes, including Kv1.4, Kv1.5, Kv2.1 and Kv4.2, were detected in rat hippocampus and cortex by RT-PCR.

RESULTS

Middle cerebral artery occlusion induced a significant neurological injury in rats. After ischemia 2 h, the mRNA of Kv1.4, Kv2.1 and Kv4.2 in hippocampus increased by 50%, 67% and 90% , respectively. And the mRNA of Kv1.4 and Kv4.2 maintained at a high level in hippocampus after ischemia 24 h. In cortex, the mRNA level of all the four subtypes were not changed significantly after ischemia 2 h, but the mRNA of Kv2.1 and Kv4.2 increased by 70% and 62% after ischemia 24 h, respectively.

CONCLUSION

The mRNA expression levels of voltage-dependent potassium channels were up-regulated in rat hippocampus and cortex after middle cerebral artery occlusion.