Voltage-sensor movements in the Eag Kv channel under an applied electric field

Voltage-dependent ion channels regulate the opening of their pores by sensing the membrane voltage. This process underlies the propagation of action potentials and other forms of electrical activity in cells. The voltage dependence of these channels is governed by the transmembrane displacement of the positive charged S4 helix within their voltage-sensor domains. We use cryo-electron microscopy to visualize this movement in the mammalian Eag voltage-dependent potassium channel in lipid membrane vesicles with a voltage difference across the membrane. Multiple structural configurations show that the applied electric field displaces S4 toward the cytoplasm by two helical turns, resulting in an extended interfacial helix near the inner membrane leaflet. The position of S4 in this down conformation is sterically incompatible with an open pore, thus explaining how movement of the voltage sensor at hyperpolarizing membrane voltages locks the pore shut in this kind of voltage-dependent K⁺ (K_v) channel. The structures solved in lipid bilayer vesicles detail the intricate interplay between K_v channels and membranes, from showing how arginines are stabilized deep within the membrane and near phospholipid headgroups, to demonstrating how the channel reshapes the inner leaflet of the membrane itself.

In voltage-dependent ion channels, the transmembrane voltage determines whether the pore opens. At the same time, the flow of ions through the open pore alters the membrane voltage by charging the membrane capacitance. This recursive regulation of ion channel activity by membrane voltage is the fundamental process at the heart of cellular electricity. As described by Hodgkin and Huxley (1), voltage-dependent membrane permeability to Na⁺ and K⁺ (ion channels as molecular entities had not yet been discovered) generates the action potential, which is by far the most rapid form of information transfer across long distances in cells. Voltage-dependent ion channels underlie many other aspects of cell signaling as well, including the initiation of muscle contraction by voltage-dependent Ca²⁺ channels (2, 3) and the control of cardiac and neuronal pacemaker frequency by the hyperpolarization-activated cyclic nucleotide–gated (HCN) channel (4, 5).Voltage-dependent ion channels contain structural domains called voltage sensors that control pore opening by membrane voltage. Whether in K⁺, Na⁺, Ca²⁺, or cation channels like HCN channels or transient receptor potential (TRP) channels, voltage sensors have a conserved structure comprising four transmembrane helices, named S1, S2, S3, and S4 (3, 6, 7). The fourth helix, S4, contains repeats of the amino acid triplet (RXX)_n, where R stands for arginine, sometimes substituted by lysine, X for hydrophobic amino acid, and n varies widely among different channels. At the center of voltage sensors, inside the membrane’s interior, a constellation of negative charged amino acids, aspartate or glutamate, and a phenylalanine residue forms a gating-charge transfer center that stabilizes the positive charged side chains of arginine and lysine as they cross the membrane (8, 9). In some voltage sensors, S4 undergoes a transition from an α to a 3₁₀ helix to direct the arginine and lysine side chains of S4 into the gating-charge transfer center (8–11). The displacement of S4 across the membrane is detectable as a nonlinear capacitive current, called gating current in electrophysiology experiments (9, 12), and is ultimately responsible for voltage control of a voltage-dependent ion channel’s pore.So far, voltage-dependent ion channel structures have been determined in crystals, detergent micelles, or nanodiscs without a voltage difference across them (8, 13–19). Under such conditions, most voltage sensors adopt a depolarized conformation, which is expected in a membrane at 0 mV. Chemical cross links, metal affinity bridges, mutations, and toxins have been used to capture or stabilize voltage sensors in conformations thought to mimic the hyperpolarized (i.e., negative voltage inside) condition (10, 11, 20–23). Here, we present a cryo-electron microscopy (cryo-EM) analysis of the mammalian Eag voltage-dependent K⁺ (K_v) channel in lipid membrane vesicles with a voltage generated across the membrane using K⁺ ion gradients in the presence of valinomycin. Doing so allows us to not only visualize how the voltage sensors respond to the applied electric field but also to see how the lipid membrane near the channel, which is intimately tied to the function of voltage-dependent ion channels, is reshaped by these conformational changes.     

Meta-analysis of self-gripping mesh (Progrip) versus sutured mesh in open inguinal hernia repair

BackgroundThis metaanalysis was designed to systematically analyse all published randomized controlled trials comparing self-gripping mesh (ProGrip) and sutured mesh to analyse early and long term outcomes for open inguinal hernia repair.MethodsA literature search was performed using the Cochrane Colorectal Cancer Group Controlled Trials Register, the Cochrane Central Register of Controlled Trials in the Cochrane Library, MEDLINE, Embase and Science Citation Index Expanded. Randomized trials comparing self-gripping mesh with sutured mesh were included. Statistical analysis was performed using Review Manager Version 5.2 software. The primary outcome measures were hernia recurrence and chronic pain after operation. Secondary outcome measures included surgical time, wound complications and perioperative complications.ResultsFive randomized trials were identified as suitable, including 1170 patients. There was no significant difference between the two types of mesh repairs in perioperative complications, wound haematoma, chronic groin pain and hernia recurrence. Wound infection was lower in self gripping mesh group compared to sutured mesh but this was not statistically significant (risk ratio (RR) 0.57, 95% confidence interval 0.30–1.06, P = 0.08). The duration of operation was significantly shorter with self-gripping mesh compared to sutured mesh with a mean difference of ?5.48 min [?9.31, ?1.64] Z = 2.80 (P = 0.005).ConclusionSelf-gripping mesh was associated with shorter operative time compared to sutured mesh. Both types of mesh repairs have comparable perioperative and long term outcomes.     

Amino acid sequence of the plasma membrane ATPase of Neurospora crassa: deduction from genomic and cDNA sequences.

The plasma membrane of Neurospora crassa contains an electrogenic H+-ATPase (EC 3.6.1.35), for which we have isolated and sequenced both genomic and cDNA clones. The ATPase gene is interrupted by four small introns (58-124 base pairs). It encodes a protein of 920 amino acids (Mr, 99,886) possessing as many as eight transmembrane segments. The Neurospora ATPase shows significant amino acid sequence homology with the Na+,K+- and Ca2+-transporting ATPases of animal cells, particularly in regions that appear to be involved in ATP binding and hydrolysis.     

Epilepsy: Asia versus Africa

Is epilepsy truly an “African ailment”? We aimed to determine this, since international health agencies often refer to epilepsy as an African disease and the scientific literature has spoken the same tone. Various published materials, mainly reports, articles, were used to gather Asian and African evidence on various aspects of epilepsy and many of its risk and associated factors. Our results suggest that in no way can epilepsy be considered as an African ailment and such characterization is most likely based on popular beliefs rather than scientific evidence. In comparison to Africa, Asia has a 5.0% greater burden from all diseases, and is 17.0% more affected from neuropsychiatric disorders (that include epilepsy). Given that more countries in Asia are transitioning, there may be large demographic and lifestyle changes in the near future. However these changes are nowhere close to those expected in Africa. Moreover, 23 million Asians have epilepsy in comparison to 3.3 million Africans and 1.2 million sub‐Saharan Africans. In comparison to Africa, Asia has more untreated patients, 55.0% more additional epilepsy cases every year, because of its larger population, with greater treatment cost and possibly higher premature mortality. Of several associated factors discussed herein, many have more importance for Asia than Africa. The current state of epilepsy in Asia is far less than ideal and there is an urgent need to recognize and accept the importance of epilepsy in Asia. In no way can epilepsy be considered as an African ailment. This is most likely based on popular beliefs rather than scientific evidence. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here .     

beta-thalassemia and gonadal axis: a cross-sectional, clinical study in a Greek population

beta-thalassemia (beta-thal) is characterized by disturbances of the reproductive system. The aim of the present study was: 1) to assess the hypothalamic- pituitary-gonadal axis in patients with beta-thal in relation to their phenotype and 2) to determine prognostic features of current gonadal status. We studied 135 patients (67 males and 68 females) with beta-thal through history, physical examination, spermiograms and GnRH test. These patients were divided into beta-thal major (51 males and 62 females) and beta-thal intermedia phenotypes (16 males and 6 females). Male patients with beta-thal major were subdivided into three groups a) eugonadal (35%, Tanner's stage V, normal testicular volume, normal spermiograms, normal basal and stimulated hormone values), b) patients with hypogonadotrophic hypogonadism (HH) of late onset (24%, Tanner's stage II-V, low-normal testicular volume, abnormal spermiograms, normal basal gonadotrophin values and abnormal response to GnRH test) and c) patients with HH of early onset (41%, Tanner's stage I, small testicular volume, abnormal spermiograms, abnormal basal and stimulated hormone values). Female patients with beta-thal major were subdivided into: a) eugonadal (32%, Tanner's stage V, regular menstruation, normal basal and stimulated hormone values), b) patients with hypogonadotrophic hypogonadism (HH) of late onset (34%, Tanner's stage II-V, secondary amenorrhea, subnormal basal and stimulated gonadotrophin values) and c) patients with HH of early onset (34%, Tanner's stage I, primary amenorrhea, subnormal basal and stimulated hormone values). Patients with beta-thal intermedia were subdivided into eugonadal (75% of males, 33% of females) and hypogonadal (25% of males, 67% of females). Current gonadal status could not be predicted by means of transfusion or chelation parameters. In conclusion, beta-thal patients could be eugonadal or develop early or late onset HH. trade mark-thal intermedia patients have a more favorable profile than beta-thal major individuals. Current gonadal status of beta-thal patients cannot be predicted by means of history, clinical or laboratory parameters.     

Correlation between peri-operative serum lactate levels and outcome in pancreatic resection for pancreatic cancer,preliminary report

This study was undertaken in order to verify if peri-operative serum lactate level changes, resulting from manipulation of the splanchnic circulation during pancreatectomy, reflected clinical outcome in twenty patients (9 males-11 females age 33 to 76) operated for pancreatic cancer. Lactate levels were evaluated at the beginning of the procedure (T0), after surgical manipulation before pancreatic resection (T1), after resection (T2), and 24 hours post-op. (T3). Furthermore, to highlight possible hemodynamic instability that could contribute to altered lactate clearance, mean arterial pressure (MAP) and central venous pressure (CVP) were continuously monitored during the study period. Peri-operative mortality within 60 days after surgery, Intensive Care Unit (ICU) length of stay, and peri-operative complications were the main indicators investigated in order to evaluate the impact of serial lactate levels in this patient population. Hyperlactatemia observed peri-operatively during pancreatic resection for cancer is significantly correlated with peri-operative mortality and also with longer ICU length of stay. Though, due to the relatively small number of the patients, more extensive investigation is needed in order to confirm such interesting preliminary data.     

How strong is the association between maternal thrombophilia and adverse pregnancy outcome? A systematic review.

OBJECTIVE: To determine whether inherited and acquired thrombophilias are associated with adverse obstetric complications. STUDY DESIGN: A systematic review; studies where women with adverse obstetric complications were tested for one or more acquired and inherited thrombophilias were included. MAIN OUTCOME MEASURES: Prevalence of thrombophilia in women with severe pre-eclampsia/eclampsia, severe placental abruption, intrauterine growth restriction or unexplained stillbirth. RESULTS: Compared with controls, placental abruption was more often associated with homozygous and heterozygous factor V Leiden mutation, heterozygous G20210A prothrombin gene mutation, homocysteinaemia, activated protein C resistance or anticardiolipin IgG antibodies. Women with pre-eclampsia/eclampsia were more likely to have heterozygous factor V Leiden mutation, heterozygous G20210A prothrombin gene mutation, homozygous MTHFR C677T mutation, protein C deficiency, protein S deficiency or activated protein C resistance compared with controls. Unexplained stillbirth, when compared with controls, was more often associated with heterozygous factor V Leiden mutation, protein S deficiency, activated protein C resistance, anticardiolipin IgG antibodies or lupus anticoagulant. Women with intrauterine growth restriction had a higher prevalence of heterozygous G20210A prothrombin gene mutation, homozygous MTHFR C677T gene mutation, protein S deficiency or anticardiolipin IgG antibodies than controls. There was wide heterogeneity in the prevalence of thrombophilia between the studies. CONCLUSIONS: Women with adverse pregnancy outcome are more likely to have a positive thrombophilia screen but studies published so far are too small to adequately assess the true size of this association. Screening for thrombophilia should not become standard practice until clear evidence emerges that thromboprophylaxis during pregnancy improves perinatal outcome. Further research into the link between the observed association, causality and heterogeneity is required.