Single Channel Analysis of Conductance and Rectification in Cation-selective, Mutant Glycine Receptor Channels

Members of the ligand-gated ion channel superfamily mediate fast synaptic transmission in the nervous system. In this study, we investigate the molecular determinants and mechanisms of ion permeation and ion charge selectivity in this family of channels by characterizing the single channel conductance and rectification of α1 homomeric human glycine receptor channels (GlyRs) containing pore mutations that impart cation selectivity. The A-1'E mutant GlyR and the selectivity double mutant ([SDM], A-1'E, P-2'Δ) GlyR, had mean inward chord conductances (at −60 mV) of 7 pS and mean outward conductances of 11 and 12 pS (60 mV), respectively. This indicates that the mutations have not simply reduced anion permeability, but have replaced the previous anion conductance with a cation one. An additional mutation to neutralize the ring of positive charge at the extracellular mouth of the channel (SDM+R19'A GlyR) made the conductance–voltage relationship linear (14 pS at both 60 and −60 mV). When this external charged ring was made negative (SDM+R19'E GlyR), the inward conductance was further increased (to 22 pS) and now became sensitive to external divalent cations (being 32 pS in their absence). The effects of the mutations to the external ring of charge on conductance and rectification could be fit to a model where only the main external energy barrier height for permeation was changed. Mean outward conductances in the SDM+R19'A and SDM+R19'E GlyRs were increased when internal divalent cations were absent, consistent with the intracellular end of the pore being flanked by fixed negative charges. This supports our hypothesis that the ion charge selectivity mutations have inverted the electrostatic profile of the pore by introducing a negatively charged ring at the putative selectivity filter. These results also further confirm the role of external pore vestibule electrostatics in determining the conductance and rectification properties of the ligand-gated ion channels

Cation-selective Mutations in the M2 Domain of the Inhibitory Glycine Receptor Channel Reveal Determinants of Ion-Charge Selectivity

Ligand-gated ion channel receptors mediate neuronal inhibition or excitation depending on their ion charge selectivity. An investigation into the determinants of ion charge selectivity of the anion-selective α1 homomeric glycine receptor (α1 glycine receptor [GlyR]) was undertaken using point mutations to residues lining the extra- and intracellular ends of the ion channel. Five mutant GlyRs were studied. A single substitution at the intracellular mouth of the channel (A-1′E GlyR) was sufficient to convert the channels to select cations over anions with PCl/PNa = 0.34. This result delimits the selectivity filter and provides evidence that electrostatic interactions between permeating ions and pore residues are a critical factor in ion charge selectivity. The P-2′Δ mutant GlyR retained its anion selectivity (PCl/PNa = 3.81), but it was much reduced compared with the wild-type (WT) GlyR (PCl/PNa = 27.9). When the A-1′E and the P-2′Δ mutations were combined (selectivity double mutant [SDM] GlyR), the relative cation permeability was enhanced (PCl/PNa = 0.13). The SDM GlyR was also Ca2+ permeable (PCa/PNa = 0.29). Neutralizing the extracellular mouth of the SDM GlyR ion channel (SDM+R19′A GlyR) produced a more Ca2+-permeable channel (PCa/PNa = 0.73), without drastically altering monovalent charge selectivity (PCl/PNa = 0.23). The SDM+R19′E GlyR, which introduces a negatively charged ring at the extracellular mouth of the channel, further enhanced Ca2+ permeability (PCa/PNa = 0.92), with little effect on monovalent selectivity (PCl/PNa = 0.19). Estimates of the minimum pore diameter of the A-1′E, SDM, SDM+R19′A, and SDM+R19′E GlyRs revealed that these pores are larger than the α1 GlyR, with the SDM-based GlyRs being comparable in diameter to the cation-selective nicotinic acetylcholine receptors. This result provides evidence that the diameter of the ion channel is also an important factor in ion charge selectivity

A Single P-loop Glutamate Point Mutation to either Lysine or Arginine Switches the Cation–Anion Selectivity of the CNGA2 Channel

Cyclic nucleotide-gated (CNG) channels play a critical role in olfactory and visual transduction. Site-directed mutagenesis and inside-out patch-clamp recordings were used to investigate ion permeation and selectivity in two mutant homomeric rat olfactory CNGA2 channels expressed in HEK293 cells. A single point mutation of the negatively charged pore loop (P-loop) glutamate (E342) to either a positively charged lysine or arginine resulted in functional channels, which consistently responded to cGMP, although the currents were generally extremely small. The concentration–response curve of the lysine mutant channel was very similar to that of wild-type (WT) channels, suggesting no major structural alteration to the mutant channels. Reversal potential measurements, during cytoplasmic NaCl dilutions, showed that the lysine and the arginine mutations switched the selectivity of the channel from cations (PCl/PNa = 0.07 [WT]) to anions (PCl/PNa = 14 [Lys] or 10 [Arg]). Relative anion permeability sequences for the two mutant channels, measured with bi-ionic substitutions, were NO3− > I− > Br− > Cl− > F− > acetate−, the same as those obtained for anion-selective GABA and glycine channels. The mutant channels also seem to have an extremely small single-channel conductance, measured using noise analysis of about 1–2 pS, compared to a WT value of about 29 pS. The results showed that it is predominantly the charge of the E342 residue in the P-loop, rather than the pore helix dipoles, which controls the cation–anion selectivity of this channel. However, the outward rectification displayed by both mutant channels in symmetrical NaCl solutions suggests that the negative ends of the pore helix dipoles may play a role in reducing the outward movement of Cl− ions through these anion-selective channels. These results have potential implications for the determinants of anion–cation selectivity in the large family of P-loop–containing channels

Final 192-week efficacy and safety results of the ADVANCE trial, comparing 3 first-line antiretroviral regimens

BACKGROUND: ADVANCE compared 3 World Health Organization-recommended first-line regimens in participants with HIV who were antiretroviral naive. METHODS: This randomized, open-label, noninferiority trial enrolled participants living with HIV with no antiretroviral exposure in the previous 6 months to 1 of the following arms: tenofovir alafenamide (TAF) / emtricitabine (FTC) + dolutegravir (DTG) (2 tablets), tenofovir disoproxil fumarate (TDF) / FTC + DTG (2 tablets), or a fixed-dose combination of TDF / FTC / efavirenz (EFV) (1 tablet). We report the final safety and efficacy data up to 192 weeks. RESULTS: Repeat consent from the original 351 participants randomized to each arm was obtained from 230 participants (66%) in the TAF/FTC + DTG arm, 209 (60%) in the TDF/FTC + DTG arm, and 183 (52%) in the TDF/FTC/EFV arm. At 192 weeks, 213 (61%) of the original 351 participants in the TAF/FTC + DTG arm, 195 (56%) in the TDF/FTC + DTG arm, and 172 (49%) in the TDF/FTC/EFV arm had confirmed RNA <50 copies/mL, with low virologic failure in all groups and no significant integrase inhibitor mutations in any arm. Mean weight gain was 8.9 kg (SD, 7.1) in the TAF/FTC + DTG arm, 5.9 kg (SD, 7.1) in the TDF/FTC + DTG arm, and 3.2 kg (SD, 8.1) in the TDF/FTC/EFV arm at 192 weeks from baseline and was greatest among women, those taking TAF, and those with lower baseline CD4 counts. The weight trajectory slowed after week 96. There were few clinical events and minor laboratory changes and differences among arms after 96 weeks. There were no significant differences in treatment-emergent hypertension or pregnancy outcomes by arm. CONCLUSIONS: High viral suppression was seen across arms, with no resistance to DTG. Weight gain continued but slowed after 96 weeks, with few clinical events or laboratory changes

ABC Transporter Genes Show Upregulated Expression in Drug Resistant Clinical Isolates of Candida auris : a Genome-Wide Characterization of ATP-Binding Cassette (ABC) Transporter Genes

Funding This work was supported by the ICMR (AMR/149/2018-ECD-II) and DBT (BT/PR14117/BRB/10/1420/2015) to RP. AKM appreciates the support by research grant EMR/2016/001927 and DST PURSE II from the Department of Science and Technology (IN). MW was grateful for a Senior Research Fellowship from the University Grant Commission. NG acknowledges the Wellcome Trust support of a Senior Investigator (101873/Z/13/Z), Collaborative (200208/A/15/Z), and Strategic Awards (097377/Z11/Z), and the MRC Centre for Medical Mycology (MR/N006364/1). AJM was supported by the University of Aberdeen studentship. Work in AL’s laboratory was supported by the Wellcome Trust (212524/Z/18/Z) and the Medical Research Council (MRC) Centre for Medical Mycology at the University of Aberdeen (MR/P501955/1 and MR/N006364/1). Acknowledgments We thank the Centre for Genome Enabled Biology and Medicine at the University of Aberdeen (E. Collie-Duguid and S. Shaw) for sequencing and support with genome analysis.Peer reviewedPublisher PD

The Pictorial Fit-Frail Scale: developing a visual scale to assess frailty

Background: Standardized frailty assessments are needed for early identification and treatment. We aimed to develop a frailty scale using visual images, the Pictorial Fit-Frail Scale (PFFS), and to examine its feasibility and content validity. Methods: In Phase 1, a multidisciplinary team identified domains for measurement, operationalized impairment levels, and re-viewed visual languages for the scale. In Phase 2, feedback was sought from health professionals and the general public. In Phase 3, 366 participants completed preliminary testing on the revised draft, including 162 UK paramedics, and rated the scale on feasibility and usability. In Phase 4, following translation into Malay, the final prototype was tested in 95 participants in Peninsular Malaysia and Borneo. Results: The final scale incorporated 14 domains, each conceptualized with 3–6 response levels. All domains were rated as “understood well” by most participants (range 64–94%). Percentage agreement with positive statements regarding appearance, feasibility, and usefulness ranged from 66% to 95%. Overall feedback from health-care professionals supported its content validity. Conclusions: The PFFS is comprehensive, feasible, and appears generalizable across countries, and has face and content validity. Investigation into the reliability and predictive validity of the scale is currently underway

Population genomics of the critically endangered kākāpō

Summary The kākāpō is a flightless parrot endemic to New Zealand. Once common in the archipelago, only 201 individuals remain today, most of them descending from an isolated island population. We report the first genome-wide analyses of the species, including a high-quality genome assembly for kākāpō, one of the first chromosome-level reference genomes sequenced by the Vertebrate Genomes Project (VGP). We also sequenced and analyzed 35 modern genomes from the sole surviving island population and 14 genomes from the extinct mainland population. While theory suggests that such a small population is likely to have accumulated deleterious mutations through genetic drift, our analyses on the impact of the long-term small population size in kākāpō indicate that present-day island kākāpō have a reduced number of harmful mutations compared to mainland individuals. We hypothesize that this reduced mutational load is due to the island population having been subjected to a combination of genetic drift and purging of deleterious mutations, through increased inbreeding and purifying selection, since its isolation from the mainland ∼10,000 years ago. Our results provide evidence that small populations can survive even when isolated for hundreds of generations. This work provides key insights into kākāpō breeding and recovery and more generally into the application of genetic tools in conservation efforts for endangered species

Internal Migration, Sport and the Scottish Diaspora in England.

Sport has been argued to play an important role for members of diasporic groups of various origins and in various locations (Burdsey, 2006; Carrington, 2010; Darby and Hassan, 2008; Kaufman, 2005). However, little attention has been paid to the role sport plays for ‘internal migrants’ who migrate to contrasting locations within a nation-state, despite the potential for significant contrasts in the prevailing sporting cultures found in different regions of the same nation-state. This article therefore aims to make a contribution towards understanding this relationship by reflecting upon the role sport plays for members of the Scottish diaspora living in England, drawing upon interviews and personal reflections from a number of Scottish ‘internal migrants’ located within the United Kingdom. In particular, discussion attempts to draw attention to the central role sport plays for these individuals in order to maintain a cultural attachment with their Scottish birthplace, given the relative lack of other cultural practices or associations which could be used to achieve this goal. Comparisons are also drawn with studies of the Scottish diaspora in more distant geographic contexts, as well as similar diasporic groups in the English context such as the Irish diaspora. These comparisons allow for a consideration of the impact of geographic proximity and cultural proximity on the relative importance of sport and other cultural practices for Scots living in England, identifying a number of important issues for those studying the role played by sport in the maintenance of a cultural attachment with ‘home’ for various diasporic groups

Understanding and responding to prescribing patterns of sodium valproate-containing medicines in pregnant women and women of childbearing age in Western Cape, South Africa

Growing evidence of the teratogenic potential of sodium valproate (VPA) has changed prescribing practices across the globe; however, the impact of this research and the consequent dissemination of a Dear Health Care Professional Letter (DHCPL) in December 2015, recommending avoidance of the teratogen VPA in women of childbearing age (WOCBA) and pregnant women in South Africa, is unknown. We explored trends and reasons for VPA use among pregnant women and WOCBA in the public sector in Western Cape Province from 1 January 2015 to 31 December 2017. Methods: Using the provincial health information exchange that collates routine electronic health data via unique patient identifiers, we analysed clinical and pharmacy records from 2015 to 2017 to determine prescription patterns of VPA and other antiepileptic drug (AED) and mood-stabilising medicine (MSM) use in WOCBA and pregnant women. Senior clinicians and policy makers were consulted to understand the determinants of VPA use. Results: At least one VPA prescription was dispensed to between 8205 (0.79%) and 9425 (0.94%) WOBCA from a cohort of approximately 1 million WOCBA attending provincial health care facilities per year