The large Ca2+-activated K+ channel (BK channel) reflects per excellence the dilemma of the molecular target driven drug discovery process. Significant experimental evidence suggests that the BK ...channels play a pivotal and specific role in many pathophysiological conditions supporting the notion that the channel represents an innovative and promising drug target. However, after more than ten years of intense research effort both in academia and industry, scientists have yet to witness the approval of a single BK channel modulator for clinical use. On the contrary, three BK openers that were progressed to clinical development have recently been discontinued (NS8, BMS204352 and TA1702) and, at the present time, only one drug candidate targeting BK channels (andolast) remains in the early phases of clinical development. Since biological studies keep strengthening the concept of BK channels as a potentially attractive target, the design and synthesis of potent and selective BK modulators continue based on novel chemical ideas. A comprehensive overview of BK channel modulators is therefore timely and important to the current medicinal chemist for review, summary, and classification of the multitude of chemical entities claimed to be BK-modulating agents. Such chemical entities are, herein, classified by both origin and chemical structure in 1) Endogenous BK channel modulators and structural analogues 2) Naturally-occurring BK channel inhibitors and blockers 3) Synthetic BK channel inhibitors and blockers 4) Marketed and/or investigational drugs with BK-modulating side properties and structural analogues 5) Naturally-occurring BK channel openers and structural analogues 6) Synthetic BK channel openers. This review is intended to provide readers with current opinion on the BK channel as a drug target, the chemical structures of BK channel modulators, the structural and chemical features involved in the BK channel modulating activity and, where and when possible, with highlights of structure – activity relationships.
About 10 distinct potassium channels in the heart are involved in shaping the action potential. Some of the K+ channels are primarily responsible for early repolarization, whereas others drive late ...repolarization and still others are open throughout the cardiac cycle. Three main K+ channels drive the late repolarization of the ventricle with some redundancy, and in atria this repolarization reserve is supplemented by the fairly atrial-specific KV1.5, Kir3, KCa, and K2P channels. The role of the latter two subtypes in atria is currently being clarified, and several findings indicate that they could constitute targets for new pharmacological treatment of atrial fibrillation. The interplay between the different K+ channel subtypes in both atria and ventricle is dynamic, and a significant up- and downregulation occurs in disease states such as atrial fibrillation or heart failure. The underlying posttranscriptional and posttranslational remodeling of the individual K+ channels changes their activity and significance relative to each other, and they must be viewed together to understand their role in keeping a stable heart rhythm, also under menacing conditions like attacks of reentry arrhythmia.
A family history of atrial fibrillation constitutes a substantial risk of developing the disease, however, the pathogenesis of this complex disease is poorly understood. We perform whole-exome ...sequencing on 24 families with at least three family members diagnosed with atrial fibrillation (AF) and find that titin-truncating variants (TTNtv) are significantly enriched in these patients (P = 1.76 × 10
). This finding is replicated in an independent cohort of early-onset lone AF patients (n = 399; odds ratio = 36.8; P = 4.13 × 10
). A CRISPR/Cas9 modified zebrafish carrying a truncating variant of titin is used to investigate TTNtv effect in atrial development. We observe compromised assembly of the sarcomere in both atria and ventricle, longer PR interval, and heterozygous adult zebrafish have a higher degree of fibrosis in the atria, indicating that TTNtv are important risk factors for AF. This aligns with the early onset of the disease and adds an important dimension to the understanding of the molecular predisposition for AF.
The Role of KChIP2 in Heart Failure
Introduction
KV4 together with KV Channel‐Interacting Protein 2 (KChIP2) mediate the fast recovering transient outward potassium current (Ito,f) in the heart. ...KChIP2 is downregulated in human heart failure (HF), potentially underlying the loss of Ito,f. We investigated remodeling associated with HF hypothesizing that KChIP2 plays a central role in the modulation of outward K+ currents in HF.
Methods and Results
HF was induced by aortic banding in wild‐type (WT) and KChIP2 deficient (KChIP2–/–) mice, evaluated by echocardiography. Action potentials were measured by floating microelectrodes in intact hearts. Ventricular cardiomyocytes were isolated and whole‐cell currents were recorded by patch clamp. Left ventricular action potentials in KChIP2–/– mice were prolonged in a rate dependent manner, consistent with patch‐clamp data showing loss of a fast recovering outward K+ current and upregulation of the slow recovering Ito,s and IKur. HF decreased all outward K+ currents in WT mice and did not change the relative contribution of Ito,f in WT mice. Compared to WT HF, KChIP2–/– HF had a larger reduction of K+‐current density. However, the relative APD prolongation caused by HF was shorter for KChIP2–/– compared with WT, and the APs of the 2 HF mouse types were indistinguishable.
Conclusion
Ito,f is just one of many K+ currents being downregulated in murine HF. The downregulation of repolarizing currents in HF is accentuated in KChIP2–/– mice. However, the prolongation of APs associated with HF is less in KChIP2–/– compared to WT, suggesting other compensatory mechanism(s) in the KChIP2–/– mouse.
Optically pumped magnetometers are becoming a promising alternative to cryogenically-cooled superconducting magnetometers for detecting and imaging biomagnetic fields. Magnetic field detection is a ...completely non-invasive method, which allows one to study the function of excitable human organs with a sensor placed outside the human body. For instance, magnetometers can be used to detect brain activity or to study the activity of the heart. We have developed a highly sensitive miniature optically pumped magnetometer based on cesium atomic vapor kept in a paraffin-coated glass container. The magnetometer is optimized for detection of biological signals and has high temporal and spatial resolution. It is operated at room- or human body temperature and can be placed in contact with or at a mm-distance from a biological object. With this magnetometer, we detected the heartbeat of an isolated guinea-pig heart, which is an animal widely used in biomedical studies. In our recordings of the magnetocardiogram, we can detect the P-wave, QRS-complex and T-wave associated with the cardiac cycle in real time. We also demonstrate that our device is capable of measuring the cardiac electrographic intervals, such as the RR- and QT-interval, and detecting drug-induced prolongation of the QT-interval, which is important for medical diagnostics.
Objectives This study investigated whether an individual's risk of developing lone atrial fibrillation (AF) before age 60 years is associated with lone AF in relatives. Background Genetic factors may ...play a role in the development of lone AF. Methods Using Danish national registers, a cohort was established of ∼4 million persons born between 1950 and 2008, and those with a family history of lone AF (AF without preceding cardiovascular/endocrine diagnoses) were identified. Individuals were followed up until the first diagnosis of lone AF. Poisson regression was used to estimate incidence rate ratios (IRRs). Results In ∼92 million person-years of follow-up, 9,507 persons were identified as having lone AF. The IRRs for lone AF given an affected first- or second-degree relative were 3.48 (95% confidence interval CI: 3.08 to 3.93) and 1.64 (95% CI: 1.04 to 2.59), respectively. IRRs were higher for men than for women but were not associated with the affected relative's sex. IRR for lone AF was 6.24 (95% CI: 2.59 to 15.0), given at least 2 first-degree relatives affected with lone AF. The IRR for lone AF in persons aged <40 years given a first-degree relative affected at age <40 years was 5.42 (95% CI: 3.80 to 7.72), and 8.53 (95% CI: 3.82 to 19.0) in persons age <30 years given a first-degree relative affected at age <30 years. Conclusions A family history of lone AF is associated with substantial risk of lone AF, with the strongest risks associated with young age at onset, multiple affected relatives, and in first-degree relatives. These results suggest routine evaluation of the families of at least certain types of patients with lone AF.
At present, transgenes in Caenorhabditis elegans are generated by injecting DNA into the germline. The DNA assembles into a semistable extrachromosomal array composed of many copies of injected DNA. ...These transgenes are typically overexpressed in somatic cells and silenced in the germline. We have developed a method that inserts a single copy of a transgene into a defined site. Mobilization of a Mos1 transposon generates a double-strand break in noncoding DNA. The break is repaired by copying DNA from an extrachromosomal template into the chromosomal site. Homozygous single-copy insertions can be obtained in less than 2 weeks by injecting approximately 20 worms. We have successfully inserted transgenes as long as 9 kb and verified that single copies are inserted at the targeted site. Single-copy transgenes are expressed at endogenous levels and can be expressed in the female and male germlines.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Key points
KCNE4 alters the biophysical properties and cellular localization of voltage‐gated potassium channel Kv7.4.
KCNE4 is expressed in a variety of arteries and, in mesenteric arteries, ...co‐localizes with Kv7.4, which is important in the control of vascular contractility.
Knockdown of KCNE4 leads to reduced Kv7.4 membrane abundance, a depolarized membrane potential and an augmented response to vasoconstrictors.
KCNE4 is a key regulator of the function and expression of Kv7.4 in vascular smooth muscle.
The KCNE ancillary subunits (KCNE1–5) significantly alter the expression and function of voltage‐gated potassium channels; however, their role in the vasculature has yet to be determined. The present study aimed to investigate the expression and function of the KCNE4 subunit in rat mesenteric arteries and to determine whether it has a functional impact on the regulation of arterial tone by Kv7 channels. In HEK cells expressing Kv7.4, co‐expression of KCNE4 increased the membrane expression of Kv7.4 and significantly altered Kv7.4 current properties. Quantitative PCR analysis of different rat arteries found that the KCNE4 isoform predominated and proximity ligation experiments showed that KCNE4 co‐localized with Kv7.4 in mesenteric artery myocytes. Morpholino‐induced knockdown of KCNE4 depolarized mesenteric artery smooth muscle cells and resulted in their increased sensitivity to methoxamine being attenuated (mean ± SEM EC50 decreased from 5.7 ± 0.63 μm to 1.6 ± 0.23 μm), which coincided with impaired effects of Kv7 modulators. When KCNE4 expression was reduced, less Kv7.4 expression was found in the membrane of the mesenteric artery myocytes. These data show that KCNE4 is consistently expressed in a variety of arteries, and knockdown of the expression product leads to reduced Kv7.4 membrane abundance, a depolarized membrane potential and an augmented response to vasoconstrictors. The present study is the first to demonstrate an integral role of KCNE4 in regulating the function and expression of Kv7.4 in vascular smooth muscle.
Key points
KCNE4 alters the biophysical properties and cellular localization of voltage‐gated potassium channel Kv7.4.
KCNE4 is expressed in a variety of arteries and, in mesenteric arteries, co‐localizes with Kv7.4, which is important in the control of vascular contractility.
Knockdown of KCNE4 leads to reduced Kv7.4 membrane abundance, a depolarized membrane potential and an augmented response to vasoconstrictors.
KCNE4 is a key regulator of the function and expression of Kv7.4 in vascular smooth muscle.
Atrial fibrillation (AF) is the most common cardiac arrhythmia, and early-onset lone AF has been linked to mutations in genes encoding ion channels. Mutations in the pore forming subunit KV4.3 ...leading to an increase in the transient outward potassium current (Ito) have previously been associated with the Brugada Syndrome. Here we aim to determine if mutations in KV4.3 or in the auxiliary subunit K(+) Channel-Interacting Protein (KChIP) 2 are associated with early-onset lone AF.
Two hundred and nine unrelated early-onset lone AF patients (<40 years) were recruited. The entire coding sequence of KCND3 and KCNIP2 was bidirectionally sequenced. One novel non-synonymous mutation A545P was found in KCND3 and was neither present in the control group (n = 432 alleles) nor in any publicly available database. The proband had onset of persistent AF at the age of 22, and no mutations in genes previously associated with AF were found. Electrophysiological analysis of KV4.3-A545P expressed in CHO-K1 cells, revealed that peak-current density was increased and the onset of inactivation was slower compared with WT, resulting in a significant gain-of-function both in the absence and the presence of KChIP2.
Gain-of-function mutations in KV4.3 have previously been described in Brugada Syndrome, however, this is the first report of a KV4.3 gain-of-function mutation in early-onset lone AF. This association of KV4.3 gain-of-function and early-onset lone AF further supports the hypothesis that increased potassium current enhances AF susceptibility.
The large conductance calcium- and voltage-activated K(+) channel (KCa1.1, BK, MaxiK) is ubiquitously expressed in the body, and holds the ability to integrate changes in intracellular calcium and ...membrane potential. This makes the BK channel an important negative feedback system linking increases in intracellular calcium to outward hyperpolarizing potassium currents. Consequently, the channel has many important physiological roles including regulation of smooth muscle tone, neurotransmitter release and neuronal excitability. Additionally, cardioprotective roles have been revealed in recent years. After a short introduction to the structure, function and regulation of BK channels, we review the small organic molecules activating BK channels and how these tool compounds have helped delineate the roles of BK channels in health and disease.