Channels (Austin, Tex.)最新文献

Voltage-gated Ca_V2.2 channels underlie the N-type current, and they regulate calcium entry at many presynaptic nerve endings to control transmitter release. A role for Ca_V2.2 channels has been well established in the transmission of sensory signals including noxious information using pharmacological and global gene knockout mouse models. However, investigation of the cell-specific actions of Ca_V2.2 channels has been difficult due to the lack of gene-dependent knockout mouse models and particularly in dissecting behavioral responses that depend on Ca_V2.2 channel activity. Here, we show the importance of Ca_V2.2 channels in Trpv1-lineage neurons in behavioral responses to sensory stimuli using Cre-dependent inactivation of the Cacna1b gene. Our work shows the cell-type specificity of Ca_V2.2 channels in mediating rapidly developing heat hypersensitivity and the utility of Cre-dependent inactivation of Cacna1b to discern cell-specific Ca_V2.2 channel functions.

The modulator pocket is a cryptic site discovered in the TREK1 (K_2P2.1) K2P channel. This pocket, located close to the selectivity filter, accommodates agonists that enhance the channel's activity. Since its discovery, equivalent sites in other K2P channels have been shown to bind various ligands, both endogenous and exogenous. In this review, we attempt to elucidate how the modulator pocket contributes to K2P channel activation. To this end, we first describe the gating mechanisms reported in the literature and rationalize their modes of action. We then highlight previous experimental and computational evidence for agonists that bind to the modulator pocket, together with mutations at this site that affect gating. Finally, we elaborate how the activation signal arising from the modulator pocket is transduced to the gates in K2P channels. In doing so, we outline a potential common modulator pocket architecture across K2P channels: a largely amphipathic structure - consistent with the expected properties of a pocket exposed at the interface between a hydrophobic membrane and the aqueous solvent - but still with some important channel-sequence-variations. This architecture and its key differences can be leveraged for the design of new selective and potent modulators.

Intraocular pressure (IOP) is dynamically regulated by the contractility and viscoelasticity of the trabecular meshwork (TM). Two recent studies identified the polymodal cation channel TRPV4 as a central mechanosensor that integrates mechanical, biochemical, and circadian signals to set the IOP levels. Pharmacological TRPV4 inhibition, global Trpv4 knockout, and conditional deletion of Trpv4 attenuated pathological ocular hypertension induced by corticosteroids, TGFβ2, or angle occlusion, as well as physiological nocturnal IOP elevation. Conversely, the selective TRPV4 agonist GSK1016790A raised IOP when injected intracamerally but lowered it when applied topically, indicating compartment-specific action. TRPV4 activation induced actomyosin contractility and ECM deposition in cultured TM cells and increased outflow resistance in biomimetic 3D scaffolds and hydrogels, with the impact reversed by TRPV4 inhibition and gene deletion. TGFβ2 strongly upregulated transcription and functional expression of TRPV4, revealing a feed-forward fibrotic loop that may contribute to myofibroblast transdifferentiation of the stressed TM. Collectively, these findings established TRPV4 as an essential mediator of TM contractility, stiffness, and IOP homeostasis. Its expression in key pressure-regulating tissues (TM, Schlemm's canal, ciliary body, and ciliary muscle) positions the channel as a convergence point for diverse glaucoma risk factors that regulate aqueous fluid production and drainage, and thus as a promising therapeutic target to lower IOP without global disruption of actin polymerization.

Neuronal function requires fine-tuned and coordinated activity of several ion channels and transporters. One member of this ensemble is the KCC2 potassium-chloride cotransporter. Because KCC2 expression is required for GABA-dependent inhibitory synaptic transmission, mutations in the gene encoding KCC2 (SLC12A5) have been linked to several diseases that also arise from defects in GABA signaling, including epilepsy, schizophrenia, and autism spectrum disorders. Although characterization of the corresponding mutant proteins is ongoing, KCC2 mutants may reside at the cell surface but lack function, they may remain trapped intracellularly and are thus unable to function at the cell surface, or they may be readily degraded. In this article, we summarize these data and emphasize the importance of protein degradation and protease activity during KCC2 quality control, i.e. the pathway that ensures only properly folded and mature KCC2 can traffic to and function at the cell surface. We also highlight how proteolysis regulates the amount of active KCC2 at the cell surface, i.e. KCC2 quantity control. Finally, because previously unidentified KCC2 mutants are continuously being discovered, we discuss the use of predictive pathogenicity algorithms to provide researchers with information on potential disease outcomes.

Obesity is an established risk factor for atrial fibrillation (AF) and is associated with hypersecretion of the adipokine chemerin. Chemerin has been linked to the AF initiation and progression predominantly through Chemokine-like receptor 1(CMKLR1)-mediated signaling. This study aimed to elucidate how activation of the chemerin-CMKLR1 contributes to atrial potassium current dysregulation in obesity-related AF. Male C57BL/6J mice were divided into high-fat diet (HFD) and low-fat diet (LFD) group. Action potentials and potassium currents were recorded by whole-cell patch-clamp electrophysiology. HFD mice exhibited significantly increased susceptibility to AF. Atrial myocytes from HFD mice showed marked shortening of action potential duration, primarily due to an increase in peak repolarizing potassium current (I_k,peak). The rise in I_K,peak density was attributed to concurrent remodeling of its components, the transient outward potassium current (I_to) and the ultrarapid delayed rectifier potassium current (I_KUr). I_to density increased from 30.13 ± 0.76 pA/pF to 35.42 ± 0.70 pA/pF at +70 mV, accompanied by a leftward shift of steady-state activation, a rightward shift of steady-state inactivation, faster recovery from inactivation, and upregulated Kv4.3 and KChIP2 expression. I_KUr density increased from 23.95 ± 1.95 pA/pF to 30.24 ± 0.97 pA/pF at +70 mV, consistent with elevated Kv1.5 expression. These electrophysiological changes were paralleled by upregulated protein abundance of chemerin and its receptor CMKLR1 in atrial myocytes, suggesting activation of the chemerin-CMKLR1 in obese mice. Obesity-associated activation of the chemerin-CMKLR1 promotes pathological potassium current remodeling, shortens atrial APD, and contributes to obesity-related AF.

Accumulation of abdominal visceral adipose tissue (VAT) is a major risk factor for cardiovascular disease. Obesity-induced endothelial dysfunction is a precursor to severe disease, and we and others have shown that arteries embedded in VAT, but not subcutaneous adipose tissue, exhibit robust endothelial dysfunction. Using a mouse model of diet-induced obesity, we recently linked VAT from obese mice to the impairment of endothelial Kir2.1, a critical regulator of endothelial function. However, the mechanism by which VAT impairs Kir2.1 is unclear. As Kir2.1 impairment is dependent on endothelial CD36, we hypothesized that lipolytic VAT induces Kir2.1 impairment through fatty acids (FA). To test this, we first treated endothelial cells with palmitic acid (PA) to determine whether the addition of exogenous FAs recapitulated our original finding of Kir2.1 dysfunction when challenged with VAT. PA inhibited Kir2.1 assessed via whole-cell patch-clamp electrophysiology, an effect that was dependent on endothelial CD36. To determine whether inhibiting VAT lipolysis prevents Kir2.1 dysfunction in the presence of VAT in obese mice and humans, VAT was pretreated with small molecule inhibitors of adipose triglyceride lipase prior to incubating endothelial cells with adipose tissue. This approach also prevented VAT-induced impairment of endothelial Kir2.1 suggesting that VAT-derived FAs may play a role. Furthermore, inhibition of lipolysis in the VAT of obese mice and humans significantly reduced endothelial FA uptake, similar to that observed when CD36 was downregulated. These findings advance our understanding of the relationship between VAT and endothelial Kir2.1 impairment and place VAT-derived FAs as potential paracrine mediators.

A growing body of preclinical evidence indicates that the inhibition of voltage-gated Cav1.3 L-type Ca²⁺ channels could be a therapeutic concept for the therapy of treatment-resistant hypertension, spinal injury and for neuroprotection in early Parkinson's disease (PD). However, available Ca²⁺-channel blockers are potent inhibitors of vascular Cav1.2 L-type channels which can cause low blood pressure as an adverse drug reaction. Therefore, Cav1.3-selective inhibitors are needed to further investigate the therapeutic potential of Cav1.3 as drug target in vivo. The bicyclic diterpene alcohol sclareol has recently been reported to exert neuroprotective properties in a mouse PD model by blocking Cav1.3 L-type channels. This study investigates the proposed Cav1.3-selectivity of sclareol compared to Cav1.2 and to other voltage-gated Ca²⁺ channels in whole-cell patch-clamp experiments. Various stimulation protocols, including dopamine neuron-like firing patterns show that sclareol is neither a subtype-selective nor a potent blocker of heterologously expressed Cav1.3 and inhibits also Cav2.3 channels. Therefore, the contribution of Cav1.3 channel inhibition for the previously reported neuroprotective effects of sclareol in a mouse PD model remains unclear. In addition, cinnarizine, a vertigo therapeutic also under investigation for inhibition of Cav1.3-mediated aldosterone-secretion, inhibits Cav1.3 channels in a frequency-dependent manner, but also without relevant selectivity with respect to Cav1.3.

Kir (inwardly rectifying potassium) channels that play key roles in maintaining potassium homeostasis, neuronal excitability, and osmoregulation have been cloned and characterized in a variety of insects. In Drosophila melanogaster, three Kir channels (dKir1 dKir2, and dKir3) have been cloned and characterized, and share significant homology with mammalian Kir channels. The dKir channels are essential for various developmental processes, such as wing patterning, by modulating bone morphogenetic protein signaling pathways. Electrophysiological studies have confirmed that Drosophila Kir channels function in a way analogous to their mammalian counterparts, indicating that their roles in cellular and developmental signaling have been evolutionarily conserved. Several Kir channels have also been identified and characterized in mosquitoes (Aedes aegypti and Anopheles gambiae). Interestingly, insect Kir channel orthologs cluster into three gene "clades" or subfamilies (Kir1, Kir2, Kir3) that are distinct from mammal Kir channels based on sequence comparisons. Insect Kir channel paralogs range from two to eight Kir channel genes per species genome representing separate gene duplication events. These differences may be attributed to distinct physiological adaptations associated with their respective taxonomic groups. The honeybee Apis mellifera genome contains two Kir channel genes, AmKir1 and AmKir2, producing six Kir channel isoforms via alternative splicing, which have been cloned and expressed in heterologous systems to study their electrophysiological properties. This review provides a comprehensive overview of current knowledge about Kir channel structures, activities, and gating as well as of their roles in insects, including evolutionary genomic aspects, molecular biology, physiological roles, and pharmacological targeting.

Potassium ion channel (K⁺ channel) is a crucial transmembrane protein found on cell membranes that plays a pivotal role in regulating various physiological processes such as cell membrane potential, action potential formation, and cellular excitability. Diabetes, a chronic metabolic disorder characterized by elevated blood glucose levels, can cause abnormal changes in the sensitivity and functioning of K⁺ channels over time. This can lead to an increase in intracellular K⁺ and Ca²⁺, disrupting normal cellular function and metabolism and resulting in a range of physiological and metabolic issues. Recent studies have uncovered the collaborative relationship between K⁺ channels auxiliary SUR1 and Kir6.2 gating, as well as the impact of K+ channel mutations such as KCNK11 Leu114Pro, KCNQ1Arg397Trp, KCNJ11Arg136Cys, KCNK16 Leu114Pro, and KCNMA1 Gly356Arg on diabetes mellitus and associated complications. Specifically, issues such as impaired cardiac repolarization, K_ATP, Kir, TALK, and K_V channel remodeling and a higher risk of arrhythmia have been emphasized. Furthermore, structural and dysfunctional K⁺ channels (K_Ca, K_V and Kir) can also affect the function of vascular endothelial and smooth muscle cells, leading to impaired vasomotor function, abnormal cell growth, and increased inflammation. These abnormalities can result in cardiovascular damage and lesions, and increase the risk of cardiovascular disease in diabetic individuals. These findings serve as a crucial foundation for a better understanding and addressing cardiovascular issues in patients with diabetes. Moreover, different drugs and treatments targeting the K⁺ channel may yield varying effects, offering promising prospects for preventing and managing diabetes and its related complications.

The hyperpolarization-activated cyclic nucleotide-gated potassium channel 4 (HCN4) gene has been reported to regulate the spontaneous depolarization of sinoatrial node cells. A novel HCN4 mutation (c.2036 G>A) may lead to sick sinus syndrome. The green fluorescent protein (GFP) and either the wild-type (WT) or C679Y mutant (mut) were co-transfected into HEK293 cells to investigate the impact of the mutation on HCN4 channel function. The whole-cell patch-clamp approach was utilized to record HCN4 currents. According to electrophysiological recording, the current amplitude and density generated by mut-C679Y HCN4 channels were much lower than those generated by WT channels. HCN4 channel current activation was not significantly affected by the C679Y mutation. Because of the little current, analyzing the mut channel deactivation kinetic was challenging. Thus, we have identified a novel HCN4 gene mutation that is connected to bradycardia, left ventricular noncompaction, and diverse valve-related heart conditions.