Search Results (40)

Pituitary cells are specialized cells located within the pituitary gland, a small, pea-sized gland situated at the base of the brain. Through the use of cellular electrophysiological techniques, the electrical properties of these cells have been revealed. This review paper aims to introduce the ion currents that are known to be functionally expressed in pituitary cells. These currents include a voltage-gated Na⁺ current (I_Na), erg-mediated K⁺ current (I_K(erg)), M-type K⁺ current (I_K(M)), hyperpolarization-activated cation current (I_h), and large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel. The biophysical characteristics of the respective ion current were described. Additionally, we also provide explanations for the effect of various drugs or compounds on each of these currents. GH₃-cell exposure to GV-58 can increase the magnitude of I_Na with a concurrent rise in the inactivation time constant of the current. The presence of esaxerenone, an antagonist of the aldosterone receptor, directly suppresses the magnitude of peak and late I_Na. Risperidone, an atypical antipsychotic agent, is effective at suppressing the I_K(erg) amplitude directly, and di(2-ethylhexyl)-phthalate suppressed I_K(erg). Solifenacin and kynurenic acid can interact with the K_M channel to stimulate I_K(M), while carisbamate and cannabidiol inhibit the I_h amplitude activated by sustained hyperpolarization. Moreover, the presence of either rufinamide or QO-40 can enhance the activity of single BK_Ca channels. To summarize, alterations in ion currents within native pituitary cells or pituitary tumor cells can influence their functional activity, particularly in processes like stimulus–secretion coupling. The effects of small-molecule modulators, as demonstrated here, bear significance in clinical, therapeutic, and toxicological contexts. Full article

Bisphenol A (BPA) is the most used widely synthetic compound for the manufacture of polycarbonate plastics and epoxy resins produced worldwide. Given its androgenic and estrogenic activities, BPA is an endocrine disruptor that is linked to neurological and vascular outcomes, including strokes. Therefore, this study aims to investigate the mechanisms by which a 24 h exposure to BPA (0.002–20 μM) modifies the contractile function of rat middle cerebral artery (MCA) smooth muscle cells (SMCs). Thus, MCA explants were isolated from Wistar rats, and the SMC-MCA vasoactive response was assessed using planar cell surface area, while the gene expression of proteins and ion channel subunits involved in the MCA vasoactive response was evaluated by real-time quantitative PCR. The exposure to BPA (0.02 and 2 μM) decreased the noradrenaline (NA) vasocontractile response and sodium nitroprusside (SNP) vasorelaxant response. Moreover, exposure to BPA (0.02 and 2 μM) increased the gene expression of the soluble guanyl cyclase protein and the large conductance Ca²⁺-activated K⁺ channels (1.1 α-subunit). These results suggest an impairment of the SMC-MCA vasoactive response induced by intermediate BPA concentrations, an effect not attained for the lowest or highest exposure concentrations (non-monotonic inverted U-shaped response). In summary, these findings suggest that BPA exposure modifies MCA vascular homeostasis by interfering with the nitric oxide (NO) pathway and may, thus, be involved in ischemic stroke development. Full article

Podocytes express large-conductance Ca²⁺-activated K⁺ channels (BK channels) and at least two different pore-forming KCa1.1 subunit C-terminal splice variants, known as VEDEC and EMVYR, along with auxiliary β and γ subunits. Podocyte KCa1.1 subunits interact directly with TRPC6 channels and BK channels become active in response to Ca²⁺ influx through TRPC6. Here, we confirmed that Ca²⁺ influx through TRPC channels is reduced following the blockade of BK channels by paxilline. The overall abundance of KCa1.1 subunits, as well as that of β4 and γ3 subunits, were increased in glomeruli isolated from Sprague Dawley rats during chronic puromycin aminonucleoside (PAN) nephrosis. Exposing cultured mouse podocytes for 24 h to recombinant TNFα, a circulating factor implicated in pediatric nephrotic syndromes, did not affect the total abundance of KCa1.1, but did evoke significant increases in both β4 and γ3. However, TNFα evoked a marked increase in the surface abundance of KCa1.1 subunits, similar to that of its previously reported effects on TRPC6 channels. The effect of TNFα on the surface expression of KCa1.1 was eliminated following siRNA knockdown of the β4 subunits, suggesting a role for this subunit in KCa1.1 trafficking to the cell surface. By contrast, treating podocytes with suPAR did not affect the total or surface expression of KCa1.1. The coordinated activation of KCa1.1 channels may promote Ca²⁺ influx through TRPC channels during normal and abnormal podocyte function by maintaining a membrane potential that allows for the efficient permeation of divalent cations through TRPC pores. Full article

This review paper delves into the current body of evidence, offering a thorough analysis of the impact of large-conductance Ca²⁺-activated K⁺ (BK_Ca or BK) channels on the electrical dynamics of the heart. Alterations in the activity of BK_Ca channels, responsible for the generation of the overall magnitude of Ca²⁺-activated K⁺ current at the whole-cell level, occur through allosteric mechanisms. The collaborative interplay between membrane depolarization and heightened intracellular Ca²⁺ ion concentrations collectively contribute to the activation of BK_Ca channels. Although fully developed mammalian cardiac cells do not exhibit functional expression of these ion channels, evidence suggests their presence in cardiac fibroblasts that surround and potentially establish close connections with neighboring cardiac cells. When cardiac cells form close associations with fibroblasts, the high single-ion conductance of these channels, approximately ranging from 150 to 250 pS, can result in the random depolarization of the adjacent cardiac cell membranes. While cardiac fibroblasts are typically electrically non-excitable, their prevalence within heart tissue increases, particularly in the context of aging myocardial infarction or atrial fibrillation. This augmented presence of BK_Ca channels’ conductance holds the potential to amplify the excitability of cardiac cell membranes through effective electrical coupling between fibroblasts and cardiomyocytes. In this scenario, this heightened excitability may contribute to the onset of cardiac arrhythmias. Moreover, it is worth noting that the substances influencing the activity of these BK_Ca channels might influence cardiac electrical activity as well. Taken together, the BK_Ca channel activity residing in cardiac fibroblasts may contribute to cardiac electrical function occurring in vivo. Full article

The modulation of K⁺ channels plays a crucial role in cell migration and proliferation, but the effect of K⁺ channels on human cutaneous wound healing (CWH) remains underexplored. This study aimed to determine the necessity of modulating K⁺ channel activity and expression for human CWH. The use of 25 mM KCl as a K⁺ channel blocker markedly improved wound healing in vitro (in keratinocytes and fibroblasts) and in vivo (in rat and porcine models). K⁺ channel blockers, such as quinine and tetraethylammonium, aided in vitro wound healing, while Ba²⁺ was the exception and did not show similar effects. Single-channel recordings revealed that the Ba²⁺-insensitive large conductance Ca²⁺-activated K⁺ (BK_Ca) channel was predominantly present in human keratinocytes. NS1619, an opener of the BK_Ca channel, hindered wound healing processes like proliferation, migration, and filopodia formation. Conversely, charybdotoxin and iberiotoxin, which are BK_Ca channel blockers, dramatically enhanced these processes. The downregulation of BK_Ca also improved CWH, whereas its overexpression impeded these healing processes. These findings underscore the facilitative effect of BK_Ca channel suppression on CWH, proposing BK_Ca channels as potential molecular targets for enhancing human cutaneous wound healing. Full article

The malignancy of glioblastoma (GBM), the most aggressive type of human brain tumor, strongly correlates with the presence of hypoxic areas within the tumor mass. Oxygen levels have been shown to control several critical aspects of tumor aggressiveness, such as migration/invasion and cell death resistance, but the underlying mechanisms are still unclear. GBM cells express abundant K⁺ and Cl⁻ channels, whose activity supports cell volume and membrane potential changes, critical for cell proliferation, migration and death. Volume-regulated anion channels (VRAC), which mediate the swelling-activated Cl⁻ current, and the large-conductance Ca²⁺-activated K⁺ channels (BK) are both functionally upregulated in GBM cells, where they control different aspects underlying GBM malignancy/aggressiveness. The functional expression/activity of both VRAC and BK channels are under the control of the oxygen levels, and these regulations are involved in the hypoxia-induced GBM cell aggressiveness. The present review will provide a comprehensive overview of the literature supporting the role of these two channels in the hypoxia-mediated GBM malignancy, suggesting them as potential therapeutic targets in the treatment of GBM. Full article

The large-conductance Ca²⁺-activated K⁺ channel, K_Ca1.1, plays a pivotal role in cancer progression, metastasis, and the acquisition of chemoresistance. Previous studies indicated that the pharmacological inhibition of K_Ca1.1 overcame resistance to doxorubicin (DOX) by down-regulating multidrug resistance-associated proteins in the three-dimensional spheroid models of human prostate cancer LNCaP, osteosarcoma MG-63, and chondrosarcoma SW-1353 cells. Investigations have recently focused on the critical roles of intratumoral, drug-metabolizing cytochrome P450 enzymes (CYPs) in chemoresistance. In the present study, we examined the involvement of CYPs in the acquisition of DOX resistance and its overcoming by inhibiting K_Ca1.1 in cancer spheroid models. Among the CYP isoforms involved in DOX metabolism, CYP3A4 was up-regulated by spheroid formation and significantly suppressed by the inhibition of K_Ca1.1 through the transcriptional repression of CCAAT/enhancer-binding protein, CEBPB, which is a downstream transcription factor of the Nrf2 signaling pathway. DOX resistance was overcome by the siRNA-mediated inhibition of CYP3A4 and treatment with the potent CYP3A4 inhibitor, ketoconazole, in cancer spheroid models. The phosphorylation levels of Akt were significantly reduced by inhibiting K_Ca1.1 in cancer spheroid models, and K_Ca1.1-induced down-regulation of CYP3A4 was reversed by the treatment with Akt and Nrf2 activators. Collectively, the present results indicate that the up-regulation of CYP3A4 is responsible for the acquisition of DOX resistance in cancer spheroid models, and the inhibition of K_Ca1.1 overcame DOX resistance by repressing CYP3A4 transcription mainly through the Akt-Nrf2-CEBPB axis. Full article

The renin–angiotensin–aldosterone system (RAAS) plays a crucial role in maintaining various physiological processes in the body, including blood pressure regulation, electrolyte balance, and overall cardiovascular health. However, any compounds or drugs known to perturb the RAAS might have an additional impact on transmembrane ionic currents. In this retrospective review article, we aimed to present a selection of chemical compounds or medications that have long been recognized as interfering with the RAAS. It is noteworthy that these substances may also exhibit regulatory effects in different types of ionic currents. Apocynin, known to attenuate the angiotensin II-induced activation of epithelial Na⁺ channels, was shown to stimulate peak and late components of voltage-gated Na⁺ current (I_Na). Esaxerenone, an antagonist of the mineralocorticoid receptor, can exert an inhibitory effect on peak and late I_Na directly. Dexamethasone, a synthetic glucocorticoid, can directly enhance the open probability of large-conductance Ca²⁺-activated K⁺ channels. Sparsentan, a dual-acting antagonist of the angiotensin II receptor and endothelin type A receptors, was found to suppress the amplitude of peak and late I_Na effectively. However, telmisartan, a blocker of the angiotensin II receptor, was effective in stimulating the peak and late I_Na along with a slowing of the inactivation time course of the current. However, telmisartan’s presence can also suppress the erg-mediated K⁺ current. Moreover, tolvaptan, recognized as an aquaretic agent that can block the vasopressin receptor, was noted to suppress the amplitude of the delayed-rectifier K⁺ current and the M-type K⁺ current directly. The above results indicate that these substances not only have an interference effect on the RAAS but also exert regulatory effects on different types of ionic currents. Therefore, to determine their mechanisms of action, it is necessary to gain a deeper understanding. Full article

Elevated TNF-α levels in serum and broncho-alveolar lavage fluid of acute lung injury patients correlate with mortality rates. We hypothesized that pharmacological plasma membrane potential (Em) hyperpolarization protects against TNF-α-induced CCL-2 and IL-6 secretion from human pulmonary endothelial cells through inhibition of inflammatory Ca²⁺-dependent MAPK pathways. Since the role of Ca²⁺ influx in TNF-α-mediated inflammation remains poorly understood, we explored the role of L-type voltage-gated Ca²⁺ (Ca_V) channels in TNF-α-induced CCL-2 and IL-6 secretion from human pulmonary endothelial cells. The Ca_V channel blocker, Nifedipine, decreased both CCL-2 and IL-6 secretion, suggesting that a fraction of Ca_V channels is open at the significantly depolarized resting Em of human microvascular pulmonary endothelial cells (−6 ± 1.9 mV), as shown by whole-cell patch-clamp measurements. To further explore the role of Ca_V channels in cytokine secretion, we demonstrated that the beneficial effects of Nifedipine could also be achieved by Em hyperpolarization via the pharmacological activation of large conductance K⁺ (BK) channels with NS1619, which elicited a similar decrease in CCL-2 but not IL-6 secretion. Using functional gene enrichment analysis tools, we predicted and validated that known Ca²⁺-dependent kinases, JNK-1/2 and p38, are the most likely pathways to mediate the decrease in CCL-2 secretion. Full article

BK channels are large conductance potassium channels characterized by four pore-forming α subunits, often co-assembled with auxiliary β and γ subunits to regulate Ca²⁺ sensitivity, voltage dependence and gating properties. BK channels are abundantly expressed throughout the brain and in different compartments within a single neuron, including axons, synaptic terminals, dendritic arbors, and spines. Their activation produces a massive efflux of K⁺ ions that hyperpolarizes the cellular membrane. Together with their ability to detect changes in intracellular Ca²⁺ concentration, BK channels control neuronal excitability and synaptic communication through diverse mechanisms. Moreover, increasing evidence indicates that dysfunction of BK channel-mediated effects on neuronal excitability and synaptic function has been implicated in several neurological disorders, including epilepsy, fragile X syndrome, mental retardation, and autism, as well as in motor and cognitive behavior. Here, we discuss current evidence highlighting the physiological importance of this ubiquitous channel in regulating brain function and its role in the pathophysiology of different neurological disorders. Full article

The Ca²⁺ ion is used ubiquitously as an intracellular signaling molecule due to its high external and low internal concentration. Many Ca²⁺-sensing ion channel proteins have evolved to receive and propagate Ca²⁺ signals. Among them are the Ca²⁺-activated potassium channels, a large family of potassium channels activated by rises in cytosolic calcium in response to Ca²⁺ influx via Ca²⁺-permeable channels that open during the action potential or Ca²⁺ release from the endoplasmic reticulum. The Ca²⁺ sensitivity of these channels allows internal Ca²⁺ to regulate the electrical activity of the cell membrane. Activating these potassium channels controls many physiological processes, from the firing properties of neurons to the control of transmitter release. This review will discuss what is understood about the Ca²⁺ sensitivity of the two best-studied groups of Ca²⁺-sensitive potassium channels: large-conductance Ca²⁺-activated K⁺ channels, K_Ca1.1, and small/intermediate-conductance Ca²⁺-activated K⁺ channels, K_Ca2.x/K_Ca3.1. Full article

The skin secretion of tree frogs contains a vast array of bioactive chemicals for repelling predators, but their structural and functional diversity is not fully understood. Paxilline (PAX), a compound synthesized by Penicillium paxilli, has been known as a specific antagonist of large conductance Ca²⁺-activated K⁺ Channels (BK_Ca). Here, we report the presence of PAX in the secretions of tree frogs (Hyla japonica) and that this compound has a novel function of inhibiting the potassium channel subfamily K member 18 (KCNK18) channels of their predators. The PAX-induced KCNK18 inhibition is sufficient to evoke Ca²⁺ influx in charybdotoxin-insensitive DRG neurons of rats. By forming π-π stacking interactions, four phenylalanines located in the central pore of KCNK18 stabilize PAX to block the ion permeation. For PAX-mediated toxicity, our results from animal assays suggest that the inhibition of KCNK18 likely acts synergistically with that of BK_Ca to elicit tingling and buzzing sensations in predators or competitors. These results not only show the molecular mechanism of PAX-KCNK18 interaction, but also provide insights into the defensive effects of the enriched PAX. Full article

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions. Full article

Rufinamide (RFM) is a clinically utilized antiepileptic drug that, as a triazole derivative, has a unique structure. The extent to which this drug affects membrane ionic currents remains incompletely understood. With the aid of patch clamp technology, we investigated the effects of RFM on the amplitude, gating, and hysteresis of ionic currents from pituitary GH₃ lactotrophs. RFM increased the amplitude of Ca²⁺-activated K⁺ currents (I_K(Ca)) in pituitary GH₃ lactotrophs, and the increase was attenuated by the further addition of iberiotoxin or paxilline. The addition of RFM to the cytosolic surface of the detached patch of membrane resulted in the enhanced activity of large-conductance Ca²⁺-activated K⁺ channels (BK_Ca channels), and paxilline reversed this activity. RFM increased the strength of the hysteresis exhibited by the BK_Ca channels and induced by an inverted isosceles-triangular ramp pulse. The peak and late voltage-gated Na⁺ current (I_Na) evoked by rapid step depolarizations were differentially suppressed by RFM. The molecular docking approach suggested that RFM bound to the intracellular domain of K_Ca1.1 channels with amino acid residues, thereby functionally affecting BK_Ca channels’ activity. This study is the first to present evidence that, in addition to inhibiting the I_Na, RFM effectively modifies the I_K(Ca), which suggests that it has an impact on neuronal function and excitability. Full article

Ewing sarcoma (EwS) is a rare and highly malignant bone tumor occurring mainly in childhood and adolescence. Physiologically, the bone is a central hub for Ca²⁺ homeostasis, which is severely disturbed by osteolytic processes in EwS. Therefore, we aimed to investigate how ion transport proteins involved in Ca²⁺ homeostasis affect EwS pathophysiology. We characterized the expression of 22 candidate genes of Ca²⁺-permeable or Ca²⁺-regulated ion channels in three EwS cell lines and found the Ca²⁺-activated K⁺ channel K_Ca2.1 (KCNN1) to be exceptionally highly expressed. We revealed that KCNN1 expression is directly regulated by the disease-driving oncoprotein EWSR1-FL1. Due to its consistent overexpression in EwS, KCNN1 mRNA could be a prognostic marker in EwS. In a large cohort of EwS patients, however, KCNN1 mRNA quantity does not correlate with clinical parameters. Several functional studies including patch clamp electrophysiology revealed no evidence for K_Ca2.1 function in EwS cells. Thus, elevated KCNN1 expression is not translated to K_Ca2.1 channel activity in EwS cells. However, we found that the low K⁺ conductance of EwS cells renders them susceptible to hypoosmotic solutions. The absence of a relevant K⁺ conductance in EwS thereby provides an opportunity for hypoosmotic therapy that can be exploited during tumor surgery. Full article