The Changes of KCNQ5 Expression and Potassium Microenvironment in the Retina of Myopic Guinea Pigs

KCNQ5 is suggestively associated with myopia, but its specific role in the myopic process has not been studied further. The aim of this study was to investigate the expression of potassium channel gene KCNQ5 and the changes of K+ microenvironment within the retina of form deprivation myopia (FDM) guinea pigs. A total of 60 guinea pigs were randomly divided into the normal control (NC) group, the self-control (SC) group, and the form-deprivation (FD) group for different treatments. Molecular assays and immunohistochemistry (IHC) were conducted to measure the expression and distribution of KCNQ5-related gene and protein in the retina. We determined the K+ concentration in the retina. In addition, the possible effects of form deprivation on potassium ionic currents and the pharmacological sensitivity of KCNQ5 activator Retigabine and inhibitor XE991 to the M-current in RPE cells were investigated using the patch-clamp technique. As a result, FD eyes exhibited more myopic refraction and longer AL. The mRNA and protein levels of KCNQ5 significantly decreased in the FD eyes, but the K+ concentration increased. In addition, the M-type K+ current [IK(M)] density decreased in FD RPE cells, and were activated or inhibited in a concentration-dependent manner due to the addition of Retigabine or XE991. Overall, KCNQ5 was significantly downregulated in the retina of FD guinea pigs, which may be associated with the increasing K+ concentration, decreasing IK(M) density, and elongating ocular axis. It suggested that KCNQ5 may play a role in the process of myopia, and the intervention of potassium channels may contribute to the prevention and control of myopia.

Activation of SGK1.1 Upregulates the M-current in the Presence of Epilepsy Mutations

In the central nervous system, the M-current plays a critical role in regulating subthreshold electrical excitability of neurons, determining their firing properties and responsiveness to synaptic input. The M-channel is mainly formed by subunits Kv7.2 and Kv7.3 that co-assemble to form a heterotetrametric channel. Mutations in Kv7.2 and Kv7.3 are associated with hyperexcitability phenotypes including benign familial neonatal epilepsy (BFNE) and neonatal epileptic encephalopathy (NEE). SGK1.1, the neuronal isoform of the serum and glucocorticoids-regulated kinase 1 (SGK1), increases M-current density in neurons, leading to reduced excitability and protection against seizures. Herein, using two-electrode voltage clamp on Xenopus laevis oocytes, we demonstrate that SGK1.1 selectively activates heteromeric Kv7 subunit combinations underlying the M-current. Importantly, activated SGK1.1 increases M-channel activity in the presence of two different epilepsy mutations found in Kv7.2, R207W and A306T. In addition, proximity ligation assays in the N2a cell line allowed us to address the effect of these mutations on Kv7-SGK1.1-Nedd4 molecular associations, a proposed pathway underlying augmentation of M-channel activity by SGK1.1

Microplastics evaluation in edible tissues of flying fish (Parexocoetus mento) from the Bintaro fish market, Lombok, Indonesia

Microplastics (MPs) are plastic fragments that are degraded into small particles with a diameter of <5 mm. Pollution in the ocean by MPs has become a global threat which damages aquatic and marine ecosystems. There are several types of MPs detected in the digestive tract and in edible fish tissue. However, such report remains limited in Indonesia. Despite the high rate of plastic pollution in Indonesian coastal areas. This study aims to determine the presence, abundance and characteristics of MPs including type, shape, and color in the edible tissue of commercially important pelagic fish species from the Bintaro fish market, Lombok, West Nusa Tenggara. Flying Fish (Parexocoetus mento) was evaluated for MPs content in their edible tissue. Isolation of MPs in fish meat was conducted by firstly adding 10% KOH solution followed by incubation for 24 h. Furthermore, the solution was incubated in the oven for 48 h at a temperature of 90oC. The WPO (Wet Peroxide Oxidation) reaction was carried out by adding 30 mL of 0.05 M Fe(II) oxide and 30 mL of 20% Hydrogen peroxide (H2O2) continued by heating on a hotplate at 75oC at 350 rpm for 45 minutes to remove organic matter from fish. The remaining filtrateswere treated by further heating, followed by filtration with stainless steel sieves (45//m). Current results show five types of MPs detected in fish sample were Fragment, Filament/fiber, Film, Foam and Pellet. The most abundant type of MPs was fragment type (368.67 particle/fish). Current results show a significant amount of MPs were found in edible tissue of flying fish in Bintaro market. However further characterization of MPs would be needed to confirm the MPs types. Nevertheless, current study show the potential contamination of MPs in P. mento fish commercially sold in fish market at Lombok, Indonesia. Hence, awareness should be raised in local communities to reduce plastic pollution in marine and coastal areas.

Activation of SGK1.1 up-regulates the M-current in the presence of epilepsy mutations

In the central nervous system, the M-current plays a critical role in regulating subthreshold electrical excitability of neurons, determining their firing properties and responsiveness to synaptic input. The M-channel is mainly formed by subunits Kv7.2 and Kv7.3 that co-assemble to form a heterotetrametric channel. Mutations in Kv7.2 and Kv7.3 are associated with hyperexcitability phenotypes including benign familial neonatal epilepsy (BFNE) and neonatal epileptic encephalopathy (NEE). SGK1.1, the neuronal isoform of the serum and glucocorticoids-regulated kinase 1 (SGK1), increases M-current density in neurons, leading to reduced excitability and protection against seizures. Herein, using two-electrode voltage clamp on Xenopus laevis oocytes, we demonstrate that SGK1.1 selectively activates heteromeric Kv7 subunit combinations underlying the M-current. Importantly, activated SGK1.1 is able to up-regulate M-channel activity in the presence of two different epilepsy mutations found in Kv7.2 subunit, R207W and A306T. In addition, proximity ligation assays in the N2a cell line allowed us to address the effect of these mutations on Kv7-SGK1.1-Nedd4 molecular associations, a proposed pathway underlying M-channel up-regulation by SGK1.1

Cannabidiol activates neuronal Kv7 channels

Cannabidiol (CBD), a chemical found in the Cannabis sativa plant, is a clinically effective antiepileptic drug whose mechanism of action is unknown. Using a fluorescence-based thallium flux assay, we performed a large-scale screen and found enhancement of flux through heterologously-expressed human Kv7.2/7.3 channels by CBD. Using patch clamp recordings, we found that CBD at low concentrations activates Kv7.2/7.3 channels at subthreshold voltages, with 100 nM CBD producing a doubling of current at -50 mV. CBD shifted the voltage-dependence of channels in the hyperpolarizing direction, producing a shift in the midpoint of activation by about ~-14 mV at 300 nM. CBD also effectively enhanced native M-current in both mouse superior cervical ganglion neurons and rat hippocampal neurons. The potent enhancement of Kv2/7.3 channels by CBD seems likely to contribute to its effectiveness as an antiepileptic drug by reducing neuronal hyperexcitability.

Alteration of Mesopontine Cholinergic Function by the Lack of KCNQ4 Subunit

The pedunculopontine nucleus (PPN), a structure known as a cholinergic member of the reticular activating system (RAS), is source and target of cholinergic neuromodulation and contributes to the regulation of the sleep–wakefulness cycle. The M-current is a voltage-gated potassium current modulated mainly by cholinergic signaling. KCNQ subunits ensemble into ion channels responsible for the M-current. In the central nervous system, KCNQ4 expression is restricted to certain brainstem structures such as the RAS nuclei. Here, we investigated the presence and functional significance of KCNQ4 in the PPN by behavioral studies and the gene and protein expressions and slice electrophysiology using a mouse model lacking KCNQ4 expression. We found that this mouse has alterations in the adaptation to changes in light–darkness cycles, representing the potential role of KCNQ4 in the regulation of the sleep–wakefulness cycle. As cholinergic neurons from the PPN participate in the regulation of this cycle, we investigated whether the cholinergic PPN might also possess functional KCNQ4 subunits. Although the M-current is an electrophysiological hallmark of cholinergic neurons, only a subpopulation of them had KCNQ4-dependent M-current. Interestingly, the absence of the KCNQ4 subunit altered the expression patterns of the other KCNQ subunits in the PPN. We also determined that, in wild-type animals, the cholinergic inputs of the PPN modulated the M-current, and these in turn can modulate the level of synchronization between neighboring PPN neurons. Taken together, the KCNQ4 subunit is present in a subpopulation of PPN cholinergic neurons, and it may contribute to the regulation of the sleep–wakefulness cycle.

The Spectrum of KCNQ2- and KCNQ3-Related Epilepsy

KCNQ genes encode for a family of six transmembrane domains, single pore-loop, and K+ channel α-subunits that have a wide range of physiological correlates. In the brain, KCNQ2 and KCNQ3 heteromultimers are thought to underlie the M-current which is essential in raising the threshold for firing an action potential; mutations in these genes may cause several types of infantile epilepsies. KCNQ2-related disorders represent a continuum of overlapping neonatal epileptic phenotypes that range from KCNQ2 benign familial neonatal epilepsy (BFNE), a seizure disorder that occur in children who typically have a normal psychomotor development and are inherited as an autosomal dominant trait, to KCNQ2 early-onset epileptic encephalopathy (EOEE) as the result of a de novo pathogenic variant. KCNQ3-related disorders are rarer and include BFNE, benign familial infantile epilepsy and KCNQ3-related epileptic encephalopathy with intellectual disability with or without seizures and/or cortical visual impairment. For both KCNQ2- and KCNQ3-related disorders, it is possible to use several drugs for different classes of mutations (i.e., gain of function vs. loss of function), and usually their effects vary in relation to the clinical presentation and the phenotype of the patient. However, KCNQ2-EOEE patients have a worse response to treatment than KCNQ2-BFNE patients and usually become drug resistant with multiple daily seizures.

Topographical Organization of M-Current on Dorsal and Median Raphe Serotonergic Neurons

Dorsal and median raphe nuclei (DR and MR, respectively) are members of the reticular activating system and play important role in the regulation of the sleep-wakefulness cycle, movement, and affective states. M-current is a voltage-gated potassium current under the control of neuromodulatory mechanisms setting neuronal excitability. Our goal was to determine the proportion of DR and MR serotonergic neurons possessing M-current and whether they are organized topographically. Electrophysiological parameters of raphe serotonergic neurons influenced by this current were also investigated. We performed slice electrophysiology on genetically identified serotonergic neurons. Neurons with M-current are located rostrally in the DR and dorsally in the MR. M-current determines firing rate, afterhyperpolarization amplitude, and adaptation index (AI) of these neurons, but does not affect input resistance, action potential width, and high threshold oscillations.These findings indicate that M-current has a strong impact on firing properties of certain serotonergic neuronal subpopulations and it might serve as an effective contributor to cholinergic and local serotonergic neuromodulatory actions.