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Cardiac small-conductance Ca2+-activated K+ (SK) channels are gated solely by beat-to-beat changes in intracellular Ca2+. Ledford et al. show distinct mechanisms by which human calmodulin mutants linked to sudden cardiac death regulate SK channels., Calmodulin (CaM) plays a critical role in intracellular signaling and regulation of Ca2+-dependent proteins and ion channels. Mutations in CaM cause life-threatening cardiac arrhythmias. Among the known CaM targets, small-conductance Ca2+-activated K+ (SK) channels are unique, since they are gated solely by beat-to-beat changes in intracellular Ca2+. However, the molecular mechanisms of how CaM mutations may affect the function of SK channels remain incompletely understood. To address the structural and functional effects of these mutations, we introduced prototypical human CaM mutations in human induced pluripotent stem cell–derived cardiomyocyte-like cells (hiPSC-CMs). Using structural modeling and molecular dynamics simulation, we demonstrate that human calmodulinopathy-associated CaM mutations disrupt cardiac SK channel function via distinct mechanisms. CaMD96V and CaMD130G mutants reduce SK currents through a dominant-negative fashion. By contrast, specific mutations replacing phenylalanine with leucine result in conformational changes that affect helix packing in the C-lobe, which disengage the interactions between apo-CaM and the CaM-binding domain of SK channels. Distinct mutant CaMs may result in a significant reduction in the activation of the SK channels, leading to a decrease in the key Ca2+-dependent repolarization currents these channels mediate. The findings in this study may be generalizable to other interactions of mutant CaMs with Ca2+-dependent proteins within cardiac myocytes.

Populations in peri-urban communities of Sub-Saharan Africa frequently depend on shallow aquifers and on-site sanitation facilities concurrently. Routinely, domestic wells end up too close to toilet facilities, risking groundwater contamination. For coastal communities, saltwater intrusion adds to the risk of groundwater contamination. This study assessed both risks in five peri-urban communities of Cape Coast, Ghana. Groundwater samples collected from 40 domestic wells were analyzed for physicochemical and microbial constituents. Multivariate statistics including hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to classify and link contaminants to potential sources. Results indicate high enteric bacteria contamination in 98% of the samples, as well as high enrichment in physicochemical constituents, tied largely to impacts of on-site sanitation facilities. We found that wells located within 25 m of septic tanks/toilet facilities contained higher contaminant loads than those without such facilities within 25 m of their locations. Similarly, for wells located close to point sources, the closer the water table is below the land surface (within 2 m), the higher the contaminant loads. Lastly, using molar ratios of Cl

SUMMARY Cardiac cells generate and amplify force in the context of cardiac load, yet the membranous sheath enclosing the muscle fibers—the sarcolemma—does not experience displacement. That the sarcolemma sustains beat-to-beat pressure changes without experiencing significant distortion is a muscle-contraction paradox. Here, we report that an elastic element—the motor protein prestin (Slc26a5)—serves to amplify actin-myosin force generation in mouse and human cardiac myocytes, accounting partly for the nonlinear capacitance of cardiomyocytes. The functional significance of prestin is underpinned by significant alterations of cardiac contractility in Prestin-knockout mice. Prestin was previously considered exclusive to the inner ear’s outer hair cells; however, our results show that prestin serves a broader cellular motor function., In brief Zhang et al. show that the motor protein prestin (Slc26a5) is expressed in the heart, serving to amplify actin-myosin force generation in cardiomyocytes. Prestin is considered to be expressed exclusively in outer hair cells of the inner ear. However, this study demonstrates prestin’s broader cellular motor function., Graphical Abstract

The mammalian cochlea relies on active electromotility of outer hair cells (OHCs) to resolve sound frequencies. OHCs use ionic channels and somatic electromotility to achieve the process. It is unclear, though, how the kinetics of voltage-gated ionic channels operate to overcome extrinsic viscous drag on OHCs at high frequency. Here, we report ultrafast electromechanical gating of clustered Kv7.4 in OHCs. Increases in kinetics and sensitivity resulting from cooperativity among clustered-Kv7.4 were revealed, using optogenetics strategies. Upon clustering, the half-activation voltage shifted negative, and the speed of activation increased relative to solitary channels. Clustering also rendered Kv7.4 channels mechanically sensitive, confirmed in consolidated Kv7.4 channels at the base of OHCs. Kv7.4 clusters provide OHCs with ultrafast electromechanical channel gating, varying in magnitude and speed along the cochlea axis. Ultrafast Kv7.4 gating provides OHCs with a feedback mechanism that enables the cochlea to overcome viscous drag and resolve sounds at auditory frequencies.

Small-conductance Ca2+-activated K+ (SK) channels regulate the excitability of cardiomyocytes by integrating intracellular Ca2+ and membrane potentials on a beat-to-beat basis. The inextricable interplay between activation of SK channels and Ca2+ dynamics suggests the pathology of one begets another. Yet, the exact mechanistic underpinning for the activation of cardiac SK channels remains unaddressed. Here, we investigated the intracellular Ca2+ microdomains necessary for SK channel activation. SK currents coupled with Ca2+ influx via L-type Ca2+ channels (LTCCs) continued to be elicited after application of caffeine, ryanodine or thapsigargin to deplete SR Ca2+ store, suggesting that LTCCs provide the immediate Ca2+ microdomain for the activation of SK channels in cardiomyocytes. Super-resolution imaging of SK2, Cav1.2 Ca2+ channel, and ryanodine receptor 2 (RyR2) was performed to quantify the nearest neighbor distances (NND) and localized the three molecules within hundreds of nanometers. The distribution of NND between SK2 and RyR2 as well as SK2 and Cav1.2 was bimodal, suggesting a spatial relationship between the channels. The activation mechanism revealed by our study paved the way for the understanding of the roles of SK channels on the feedback mechanism to regulate the activities of LTCCs and RyR2 to influence local and global Ca2+ signaling.

This paper revisited the crude oil – stock market nexus to examine how the oil implied volatility index (a forward-looking and more accurate measure for uncertainty in oil prices) affects stock returns in major Africa's oil-importing (South Africa, Kenya, Mauritius, and Botswana) and oil-exporting (Nigeria, Egypt, Tunisia, and Morocco) countries during the COVID-19 pandemic. Quantile regression is employed to examine the heterogeneous relationship at different distributions of stock returns. The study documents evidence to support a negative relationship between the oil implied volatility shocks and stock returns in the selected stock markets, especially in downturns. Findings from this study also reveal that the oil implied volatility shocks can asymmetrically influence Africa's stocks. Specifically, our empirical evidence reveals that positive shocks in the oil implied volatility index play a key role in most of Africa's stock markets in market downturns while negative shocks play a moderate role during benign market conditions in some of Africa's stock markets during the pandemic. More importantly, our findings divulge that investors can find an invaluable shelter with a portfolio of the selected African stocks and oil market securities in the time of the pandemic. The policy implications are further discussed.

Cav3 channels play a critical role in maintaining calcium homeostasis, and its dysregulation is related to age-related diseases, such as age-related hearing loss (AHL). However, the underlying mechanism of the Cav3 channels involved in AHL remains unknown. Previous studies have shown that the degeneration of spiral ganglion neurons (SGNs) plays a critical role in AHL. Here, we explored the involvement of Cav3 channels in the dysregulation of SGNs in AHL. We used C57BL/6 mice as the AHL mouse model and found that the expression of Cav3 channels was increased in SGNs associated with age. The three subtypes of Cav3 channels were present in the apical, middle, and basal SGNs from young and older (AHL) mice. The immunostaining data suggest that Cav3.1 and Cav3.2 may contribute to Cav3 upregulation in SGNs of AHL mice. Additionally, we found that calpain-2 and apoptosis-inducing factor (AIF) were activated in SGNs from AHL mice. The inhibition of Cav3 channels or calpain-2 reduced AIF-activation in SGNs may affect neuronal survival. In conclusion, the findings suggest that Cav3 channels are upregulated in SGNs from AHL mice that may contribute to the degeneration of SGNs through the calpain-2-AIF apoptosis pathway in AHL mice.

Background Globally, about 810 women die every day due to pregnancy and its related complications. Although the death of women during pregnancy or childbirth has declined from 342 deaths to 211 deaths per 100,000 live births between 2000 and 2017, maternal mortality is still higher, particularly in sub-Saharan Africa and South Asia, where 86% of all deaths occur. Methods A secondary analysis was carried out using the 2014 Ghana Demographic and Health Survey. A sample total of 4,290 women who had a live birth in the 5 years preceding the survey was included in the analysis. GIS software was used to explore the spatial distribution of unskilled birth attendance in Ghana. The Geographic Weighted Regression (GWR) was employed to model the spatial relationship of some predictor of unskilled birth attendance. Moreover, a multilevel binary logistic regression model was fitted to identify factors associated with unskilled birth attendance. Results In this study, unskilled birth attendance had spatial variations across the country. The hotspot, cluster and outlier analysis identified the concerned districts in the north-eastern part of Ghana. The GWR analysis identified different predictors of unskilled birth attendance across districts of Ghana. In the multilevel analysis, mothers with no education, no health insurance coverage, and mothers from households with lower wealth status had higher odds of unskilled birth attendance. Being multi and grand multiparous, perception of distance from the health facility as not a big problem, urban residence, women residing in communities with medium and higher poverty level had lower odds of unskilled birth attendance. Conclusion Unskilled birth attendance had spatial variations across the country. Areas with high levels of unskilled birth attendance had mothers who had no formal education, not health insured, mothers from poor households and communities, primiparous women, mothers from remote and border districts could get special attention in terms of allocation of resources including skilled human power, and improved access to health facilities.

The normal function of ion channels depends critically on the precise subcellular localization and the number of channel proteins on the cell surface membrane. Small-conductance, Ca2+-activated K+ channels (SK, KCa2) are expressed in human atrial myocytes and responsible for shaping atrial action potentials. Understanding the mechanisms of SK channel trafficking may provide new insights into the regulation controlling the repolarization of atrial myocytes. We have previously demonstrated that the C and N termini of SK2 channels interact with actin-binding proteins, α-actinin2 and filamin A, respectively. However, the roles of the interacting proteins on SK2 channel trafficking remain incompletely understood. Using Total Internal Reflection Fluorescence (TIRF) microscopy, we studied the mechanisms of surface membrane localization of SK2 (KCa2.2) channels. When SK2 channels were co-expressed with filamin A or α-actinin2, the membrane fluorescence intensity of SK2 channels increased significantly. We next tested the effects of primaquine and dynasore on SK2 channels expression. Treatment with primaquine significantly reduced the membrane expression of SK2 channels. In contrast, treatment with dynasore failed to alter the surface membrane expression of SK2 channels. Further investigations using constitutively-active or dominant-negative forms of Rab GTPases provided additional insights into the distinct roles of the two cytoskeletal proteins on the recycling processes of SK2 channels from endosomes. α-actinin2 facilitated recycling of SK2 channels from both early and recycling endosomes while filamin A likely aids the recycling of SK2 channels from recycling endosomes. This article is protected by copyright. All rights reserved

Acquired mechanical sensitivity of clustered Kv7.4 in outer hair cell sculpts fast cycle-by-cycle sound amplification and tuning., The mammalian cochlea relies on active electromotility of outer hair cells (OHCs) to resolve sound frequencies. OHCs use ionic channels and somatic electromotility to achieve the process. It is unclear, though, how the kinetics of voltage-gated ionic channels operate to overcome extrinsic viscous drag on OHCs at high frequency. Here, we report ultrafast electromechanical gating of clustered Kv7.4 in OHCs. Increases in kinetics and sensitivity resulting from cooperativity among clustered-Kv7.4 were revealed, using optogenetics strategies. Upon clustering, the half-activation voltage shifted negative, and the speed of activation increased relative to solitary channels. Clustering also rendered Kv7.4 channels mechanically sensitive, confirmed in consolidated Kv7.4 channels at the base of OHCs. Kv7.4 clusters provide OHCs with ultrafast electromechanical channel gating, varying in magnitude and speed along the cochlea axis. Ultrafast Kv7.4 gating provides OHCs with a feedback mechanism that enables the cochlea to overcome viscous drag and resolve sounds at auditory frequencies.

Potassium (K+) channels shape the response properties of neurons. Although enormous progress has been made to characterize K+ channels in the primary auditory neurons, the molecular identities of many of these channels and their contributions to hearing in vivo remain unknown. Using a combination of RNA sequencing and single molecule fluorescent in situ hybridization, we localized expression of transcripts encoding the sodium-activated potassium channels KNa1.1 (SLO2.2/Slack) and KNa1.2 (SLO2.1/Slick) to the primary auditory neurons (spiral ganglion neurons, SGNs). To examine the contribution of these channels to function of the SGNs in vivo, we measured auditory brainstem responses in KNa1.1/1.2 double knockout (DKO) mice. Although auditory brainstem response (wave I) thresholds were not altered, the amplitudes of suprathreshold responses were reduced in DKO mice. This reduction in amplitude occurred despite normal numbers and molecular architecture of the SGNs and their synapses with the inner hair cells. Patch clamp electrophysiology of SGNs isolated from DKO mice displayed altered membrane properties, including reduced action potential thresholds and amplitudes. These findings show that KNa1 channel activity is essential for normal cochlear function and suggest that early forms of hearing loss may result from physiological changes in the activity of the primary auditory neurons.

Summary Ninety percent of Americans consume less than the estimated average requirements of dietary vitamin E (vitE). Severe vitE deficiency due to genetic mutations in the tocopherol transfer protein (TTPA) in humans results in ataxia with vitE deficiency (AVED), with proprioceptive deficits and somatosensory degeneration arising from dorsal root ganglia neurons (DRGNs). Single-cell RNA-sequencing of DRGNs was performed in Ttpa−/− mice, an established model of AVED. In stark contrast to expected changes in proprioceptive neurons, Ttpa−/− DRGNs showed marked upregulation of voltage-gated Ca2+ and K+ channels in mechanosensitive, tyrosine-hydroxylase positive (TH+) DRGNs. The ensuing significant conductance changes resulted in reduced excitability in mechanosensitive Ttpa−/− DRGNs. A highly supplemented vitE diet (600 mg dl-α-tocopheryl acetate/kg diet) prevented the cellular and molecular alterations and improved mechanosensation. VitE deficiency profoundly alters the molecular signature and functional properties of mechanosensitive TH+ DRGN, representing an intriguing shift of the prevailing paradigm from proprioception to mechanical sensation., Graphical Abstract, Highlights • vitE deficiency alters gene expression in DRGs • Mechanosensitive TH+ DRG neurons are most affected • K+ and Ca2+ current densities are increased in vitE-deficient TH+ DRG neurons • High-dose vitE supplementation prevents the molecular phenotype, Neuroscience; Molecular Neuroscience; Transcriptomics