Activation of calcium- and voltage-gated potassium channels of large conductance by leukotriene B4

Insights into Leishmania donovani potassium channel family and their biological functions

Leishmania donovani is the causative organism for visceral leishmaniasis. Although this parasite was discovered over a century ago, nothing is known about role of potassium channels in L. donovani. Potassium channels are known for their crucial roles in cellular functions in other organisms. Recently the presence of a calcium-activated potassium channel in L. donovani was reported which prompted us to look for other proteins which could be potassium channels and to investigate their possible physiological roles. Twenty sequences were identified in L. donovani genome and subjected to estimation of physio-chemical properties, motif analysis, localization prediction and transmembrane domain analysis. Structural predictions were also done. The channels were majorly α-helical and predominantly localized in cell membrane and lysosomes. The signature selectivity filter of potassium channel was present in all the sequences. In addition to the conventional potassium channel activity, they were associated with gene ontology terms for mitotic cell cycle, cell death, modulation by virus of host process, cell motility etc. The entire study indicates the presence of potassium channel families in L. donovani which may have involvement in several cellular pathways. Further investigations on these putative potassium channels are needed to elucidate their roles in Leishmania.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03692-y.

Discovery of agonist-antagonist pairs for the modulation of Ca [2]+ and voltage-gated K+ channels of large conductance that contain beta1 subunits

Large conductance, calcium/voltage-gated potassium channels (BK) regulate critical body processes, including neuronal, secretory and smooth muscle (SM) function. While BK-forming alpha subunits are ubiquitous, accessory beta1 subunits are highly expressed in SM. This makes beta1 an attractive target for pharmaceutical development to treat SM disorders, such as hypertension or cerebrovascular spasm. Compounds activating BK via beta1 have been identified, yet they exhibit low potency and off-target effects while antagonists that limit agonist activity via beta 1 remain unexplored. Beta1-dependent BK ligand-based pharmacophore modeling and ZINC database searches identified 15 commercially available hits. Concentration-response curves on BK alpha + beta1 subunit-mediated currents were obtained in CHO cells. One potent (EC50 = 20 nM) and highly efficacious activator (maximal activation = ×10.3 of control) was identified along with a potent antagonist (KB = 3.02 nM), both of which were dependent on beta1. Our study provides the first proof-of-principle that an agonist/antagonist pair can be used to control beta1-containing BK activity.

The Role of Bile Acids in Cardiovascular Diseases: from Mechanisms to Clinical Implications

Bile acids (BAs), key regulators in the metabolic network, are not only involved in lipid digestion and absorption but also serve as potential therapeutic targets for metabolic disorders. Studies have shown that cardiac dysfunction is associated with abnormal BA metabolic pathways. As ligands for several nuclear receptors and membrane receptors, BAs systematically regulate the homeostasis of metabolism and participate in cardiovascular diseases (CVDs), such as myocardial infarction, diabetic cardiomyopathy, atherosclerosis, arrhythmia, and heart failure. However, the molecular mechanism by which BAs trigger CVDs remains controversial. Therefore, the regulation of BA signal transduction by modulating the synthesis and composition of BAs is an interesting and novel direction for potential therapies for CVDs. Here, we mainly summarized the metabolism of BAs and their role in cardiomyocytes and noncardiomyocytes in CVDs. Moreover, we comprehensively discussed the clinical prospects of BAs in CVDs and analyzed the clinical diagnostic and application value of BAs. The latest development prospects of BAs in the field of new drug development are also prospected. We aimed to elucidate the underlying mechanism of BAs treatment in CVDs, and the relationship between BAs and CVDs may provide new avenues for the prevention and treatment of these diseases.

The Large-Conductance, Calcium-Activated Potassium Channel: A Big Key Regulator of Cell Physiology

Large-conductance Ca²⁺-activated K⁺ channels facilitate the efflux of K⁺ ions from a variety of cells and tissues following channel activation. It is now recognized that BK channels undergo a wide range of pre- and post-translational modifications that can dramatically alter their properties and function. This has downstream consequences in affecting cell and tissue excitability, and therefore, function. While finding the “silver bullet” in terms of clinical therapy has remained elusive, ongoing research is providing an impressive range of viable candidate proteins and mechanisms that associate with and modulate BK channel activity, respectively. Here, we provide the hallmarks of BK channel structure and function generally, and discuss important milestones in the efforts to further elucidate the diverse properties of BK channels in its many forms.

Comparison of K+ Channel Families

K⁺ channels enable potassium to flow across the membrane with great selectivity. There are four K⁺ channel families: voltage-gated K (K_v), calcium-activated (K_Ca), inwardly rectifying K (K_ir), and two-pore domain potassium (K_2P) channels. All four K⁺ channels are formed by subunits assembling into a classic tetrameric (4x1P = 4P for the K_v, K_Ca, and K_ir channels) or tetramer-like (2x2P = 4P for the K_2P channels) architecture. These subunits can either be the same (homomers) or different (heteromers), conferring great diversity to these channels. They share a highly conserved selectivity filter within the pore but show different gating mechanisms adapted for their function. K⁺ channels play essential roles in controlling neuronal excitability by shaping action potentials, influencing the resting membrane potential, and responding to diverse physicochemical stimuli, such as a voltage change (K_v), intracellular calcium oscillations (K_Ca), cellular mediators (K_ir), or temperature (K_2P).

ATP-sensitive potassium channel subunits in the neuroinflammation: novel drug targets in neurodegenerative disorders

Arachidonic acids and its metabolites modulate plenty of ligand-gated, voltage-dependent ion channels, and metabolically regulated potassium channels including ATP-sensitive potassium channels (KATP). KATP channels are hetero-multimeric complexes of sulfonylureas receptors (SUR1, SUR2A or SUR2B) and the pore-forming subunits (Kir6.1 and Kir6.2) likewise expressed in the pre-post synapsis of neurons and inflammatory cells, thereby affecting their proliferation and activity. KATP channels are involved in amyloid-β (Aβ)-induced pathology, therefore emerging as therapeutic targets against Alzheimer's and related diseases. The modulation of these channels can represent an innovative strategy for the treatment of neurodegenerative disorders; nevertheless, the currently available drugs are not selective for brain KATP channels and show contrasting effects. This phenomenon can be a consequence of the multiple physiological roles of the different varieties of KATP channels. Openings of cardiac and muscular KATP channel subunits, is protective against caspase-dependent atrophy in these tissues and some neurodegenerative disorders, whereas in some neuroinflammatory diseases benefits can be obtained through the inhibition of neuronal KATP channel subunits. For example, glibenclamide exerts an anti-inflammatory effect in respiratory, digestive, urological, and central nervous system (CNS) diseases, as well as in ischemia-reperfusion injury associated with abnormal SUR1-Trpm4/TNF-α or SUR1-Trpm4/ Nos2/ROS signaling. Despite this strategy is promising, glibenclamide may have limited clinical efficacy due to its unselective blocking action of SUR2A/B subunits also expressed in cardiovascular apparatus with pro-arrhythmic effects and SUR1 expressed in pancreatic beta cells with hypoglycemic risk. Alternatively, neuronal selective dual modulators showing agonist/antagonist actions on KATP channels can be an option.

Overview of Bile Acids Signaling and Perspective on the Signal of Ursodeoxycholic Acid, the Most Hydrophilic Bile Acid, in the Heart

Bile acids (BA) are classically known as an important agent in lipid absorption and cholesterol metabolism. Nowadays, their role in glucose regulation and energy homeostasis are widely reported. BAs are involved in various cellular signaling pathways, such as protein kinase cascades, cyclic AMP (cAMP) synthesis, and calcium mobilization. They are ligands for several nuclear hormone receptors, including farnesoid X-receptor (FXR). Recently, BAs have been shown to bind to muscarinic receptor and Takeda G-protein-coupled receptor 5 (TGR5), both G-protein-coupled receptor (GPCR), independent of the nuclear hormone receptors. Moreover, BA signals have also been elucidated in other nonclassical BA pathways, such as sphingosine-1-posphate and BK (large conductance calcium- and voltage activated potassium) channels. Hydrophobic BAs have been proven to affect heart rate and its contraction. Elevated BAs are associated with arrhythmias in adults and fetal heart, and altered ratios of primary and secondary bile acid are reported in chronic heart failure patients. Meanwhile, in patients with liver cirrhosis, cardiac dysfunction has been strongly linked to the increase in serum bile acid concentrations. In contrast, the most hydrophilic BA, known as ursodeoxycholic acid (UDCA), has been found to be beneficial in improving peripheral blood flow in chronic heart failure patients and in protecting the heart against reperfusion injury. This review provides an overview of BA signaling, with the main emphasis on past and present perspectives on UDCA signals in the heart.

Large conductance voltage- and calcium-gated potassium channels (BK) in cerebral artery myocytes of perinatal fetal primates share several major characteristics with the adult phenotype

Large conductance voltage- and calcium-gated channels (BK) control fundamental processes, including smooth muscle contractility and artery diameter. We used a baboon (Papio spp) model of pregnancy that is similar to that of humans to characterize BK channels in the middle cerebral artery and its branches in near-term (165 dGa) primate fetuses and corresponding pregnant mothers. In cell-attached patches (K+pipette = 135 mM) on freshly isolated fetal cerebral artery myocytes, BK currents were identified by large conductance, and voltage- and paxilline-sensitive effects. Their calcium sensitivity was confirmed by a lower Vhalf (transmembrane voltage needed to reach half-maximal current) in inside-out patches at 30 versus 3 μM [Ca2+]free. Immunostaining against the BK channel-forming alpha subunit revealed qualitatively similar levels of BK alpha protein-corresponding fluorescence in fetal and maternal myocytes. Fetal and maternal BK currents recorded at 3 μM [Ca2+]free from excised membrane patches had similar unitary current amplitude, and Vhalf. However, subtle differences between fetal and maternal BK channel phenotypes were detected in macroscopic current activation kinetics. To assess BK function at the organ level, fetal and maternal artery branches were pressurized in vitro at 30 mmHg and probed with the selective BK channel blocker paxilline (1 μM). The degree of paxilline-induced constriction was similar in fetal and maternal arteries, yet the constriction of maternal arteries was achieved sooner. In conclusion, we present a first identification and characterization of fetal cerebral artery BK channels in myocytes from primates. Although differences in BK channels between fetal and maternal arteries exist, the similarities reported herein advance the idea that vascular myocyte BK channels are functional near-term, and thus may serve as pharmacological targets during the perinatal-neonatal period.

How lipids contribute to ion channel function, a fat perspective on direct and indirect interactions

Membrane lipid composition and remodeling influence the function of ion channels. Polyunsaturated fatty acids (PUFAs) and their derivatives modulate ion channel function; whether this effect occurs directly by binding to the protein or indirectly through alteration of membranes' mechanical properties has been difficult to distinguish. There are a large number of studies addressing the effect of fatty acids; recent structural and functional analyses have identified binding sites and provided further evidence for the role of the plasma membrane in ion channel function. Here, we review cation channels that do not share a common topology or lipid-binding signature sequence, but for which there are recent compelling data that support both direct and indirect modulation by PUFAs or their derivatives.

Calcium- and voltage-gated BK channels in vascular smooth muscle

Ion channels in vascular smooth muscle regulate myogenic tone and vessel contractility. In particular, activation of calcium- and voltage-gated potassium channels of large conductance (BK channels) results in outward current that shifts the membrane potential toward more negative values, triggering a negative feed-back loop on depolarization-induced calcium influx and SM contraction. In this short review, we first present the molecular basis of vascular smooth muscle BK channels and the role of subunit composition and trafficking in the regulation of myogenic tone and vascular contractility. BK channel modulation by endogenous signaling molecules, and paracrine and endocrine mediators follows. Lastly, we describe the functional changes in smooth muscle BK channels that contribute to, or are triggered by, common physiological conditions and pathologies, including obesity, diabetes, and systemic hypertension.

Deoxycholylglycine, a conjugated secondary bile acid, reduces vascular tone by attenuating Ca2+ sensitivity via rho kinase pathway

Patients with cirrhosis have reduced systemic vascular resistance and elevated circulating bile acids (BAs). Previously, we showed that secondary conjugated BAs impair vascular tone by reducing vascular smooth muscle cell (VSMC) Ca²⁺ influx. In this study, we investigated the effect of deoxycholylglycine (DCG), on Ca²⁺ sensitivity in reducing vascular tone. First, we evaluated the effects of DCG on U46619- and phorbol-myristate-acetate (PMA)-induced vasoconstriction. DCG reduced U46619-induced vascular tone but failed to reduce PMA-induced vasoconstriction. Then, by utilizing varied combinations of diltiazem (voltage-dependent Ca²⁺ channel [VDCC] inhibitor), Y27632 (RhoA kinase [ROCK] inhibitor) and chelerythrine (PKC inhibitor) for the effect of DCG on U46619-induced vasoconstriction, we ascertained that DCG inhibits VDCC and ROCK pathway with no effect on PKC. We further assessed the effect of DCG on ROCK pathway. In β-escin-permeabilized arteries, DCG reduced high-dose Ca²⁺- and GTPγS (a ROCK activator)-induced vasoconstriction. In rat vascular smooth muscle cells (VSMCs), DCG reduced U46619-induced phosphorylation of myosin light chain subunit (MLC₂₀) and myosin phosphatase target subunit-1 (MYPT1). In permeabilized VSMCs, DCG reduced Ca²⁺- and GTPγS-mediated MLC₂₀ and MYPT1 phosphorylation, and further, reduced GTPγS-mediated membrane translocation of RhoA. In VSMCs, long-term treatment with DCG had no effect on ROCK2 and RhoA expression. In conclusion, DCG attenuates vascular Ca²⁺ sensitivity and tone via inhibiting ROCK pathway. These results enhance our understanding of BAs-mediated regulation of vascular tone and provide a platform to develop new treatment strategies to reduce arterial dysfunction in cirrhosis.

Regulation of Ca2+-Sensitive K+ Channels by Cholesterol and Bile Acids via Distinct Channel Subunits and Sites

Cholesterol (CLR) conversion into bile acids (BAs) in the liver constitutes the major pathway for CLR elimination from the body. Moreover, these steroids regulate each other's metabolism. While the roles of CLR and BAs in regulating metabolism and tissue function are well known, research of the last two decades revealed the existence of specific protein receptors for CLR or BAs in tissues with minor contribution to lipid metabolism, raising the possibility that these lipids serve as signaling molecules throughout the body. Among other lipids, CLR and BAs regulate ionic current mediated by the activity of voltage- and Ca²⁺-gated, K⁺ channels of large conductance (BK channels) and, thus, modulate cell physiology and participate in tissue pathophysiology. Initial work attributed modification of BK channel function by CLR or BAs to the capability of these steroids to directly interact with bilayer lipids and thus alter the physicochemical properties of the bilayer with eventual modification of BK channel function. Based on our own work and that of others, we now review evidence that supports direct interactions between CLR or BA and specific BK protein subunits, and the consequence of such interactions on channel activity and organ function, with a particular emphasis on arterial smooth muscle. For each steroid type, we will also briefly discuss several mechanisms that may underlie modification of channel steady-state activity. Finally, we will present novel computational data that provide a chemical basis for differential recognition of CLR vs lithocholic acid by distinct BK channel subunits and recognition sites.

Modulation of BK Channel Function by Auxiliary Beta and Gamma Subunits

The large-conductance, Ca(2+)- and voltage-activated K(+) (BK) channel is ubiquitously expressed in mammalian tissues and displays diverse biophysical or pharmacological characteristics. This diversity is in part conferred by channel modulation with different regulatory auxiliary subunits. To date, two distinct classes of BK channel auxiliary subunits have been identified: β subunits and γ subunits. Modulation of BK channels by the four auxiliary β (β1-β4) subunits has been well established and intensively investigated over the past two decades. The auxiliary γ subunits, however, were identified only very recently, which adds a new dimension to BK channel regulation and improves our understanding of the physiological functions of BK channels in various tissues and cell types. This chapter will review the current understanding of BK channel modulation by auxiliary β and γ subunits, especially the latest findings.