Crystal structure of a voltage-gated sodium channel in two potentially inactivated states

In excitable cells, voltage-gated sodium (Na(V)) channels activate to initiate action potentials and then undergo fast and slow inactivation processes that terminate their ionic conductance. Inactivation is a hallmark of Na(V) channel function and is critical for control of membrane excitability, but the structural basis for this process has remained elusive. Here we report crystallographic snapshots of the wild-type Na(V)Ab channel from Arcobacter butzleri captured in two potentially inactivated states at 3.2?? resolution. Compared to previous structures of Na(V)Ab channels with cysteine mutations in the pore-lining S6 helices (ref. 4), the S6 helices and the intracellular activation gate have undergone significant rearrangements: one pair of S6 helices has collapsed towards the central pore axis and the other S6 pair has moved outward to produce a striking dimer-of-dimers configuration. An increase in global structural asymmetry is observed throughout our wild-type Na(V)Ab models, reshaping the ion selectivity filter at the extracellular end of the pore, the central cavity and its residues that are analogous to the mammalian drug receptor site, and the lateral pore fenestrations. The voltage-sensing domains have also shifted around the perimeter of the pore module in wild-type Na(V)Ab, compared to the mutant channel, and local structural changes identify a conserved interaction network that connects distant molecular determinants involved in Na(V) channel gating and inactivation. These potential inactivated-state structures provide new insights into Na(V) channel gating and novel avenues to drug development and therapy for a range of debilitating Na(V) channelopathies.     

Mutations in GRIN2A and GRIN2B encoding regulatory subunits of NMDA receptors cause variable neurodevelopmental phenotypes

N-methyl-D-aspartate (NMDA) receptors mediate excitatory neurotransmission in the mammalian brain. Two glycine-binding NR1 subunits and two glutamate-binding NR2 subunits each form highly Ca2(+)-permeable cation channels which are blocked by extracellular Mg2(+) in a voltage-dependent manner. Either GRIN2B or GRIN2A, encoding the NMDA receptor subunits NR2B and NR2A, was found to be disrupted by chromosome translocation breakpoints in individuals with mental retardation and/or epilepsy. Sequencing of GRIN2B in 468 individuals with mental retardation revealed four de novo mutations: a frameshift, a missense and two splice-site mutations. In another cohort of 127 individuals with idiopathic epilepsy and/or mental retardation, we discovered a GRIN2A nonsense mutation in a three-generation family. In a girl with early-onset epileptic encephalopathy, we identified the de novo GRIN2A mutation c.1845C>A predicting the amino acid substitution p.N615K. Analysis of NR1-NR2A(N615K) (NR2A subunit with the p.N615K alteration) receptor currents revealed a loss of the Mg2(+) block and a decrease in Ca2(+) permeability. Our findings suggest that disturbances in the neuronal electrophysiological balance during development result in variable neurological phenotypes depending on which NR2 subunit of NMDA receptors is affected.     

Regulatory circuits controlling vascular cell calcification

Vascular calcification is a common feature of chronic kidney disease, cardiovascular disease, and aging. Such abnormal calcium deposition occurs in medial and/or intimal layers of blood vessels as well as in cardiac valves. Once considered a passive and inconsequential finding, the presence of calcium deposits in the vasculature is widely accepted as a predictor of increased morbidity and mortality. Recognition of the importance of vascular calcification in health is driving research into mechanisms that govern its development, progression, and regression. Diverse, but highly interconnected factors, have been implicated, including disturbances in lipid metabolism, oxidative stress, inflammatory cytokines, and mineral and hormonal balances, which can lead to formation of osteoblast-like cells in the artery wall. A tight balance of procalcific and anticalcific regulators dictates the extent of disease. In this review, we focus on the main regulatory circuits modulating vascular cell calcification.     

Total thyroidectomy is safer with identification of recurrent laryngeal nerve

Objective： To investigate the effect of recurrent laryngeal nerve （RLN） identification on the complications after total thyroidectomy and lobectomy. Methods： Total 134 consecutive patients undergoing total thyroidectomy or thyroid lobectomy from January 2003 to November 2004 were investigated retrospectively. Patients were divided into two groups： RLN identified （Group A） or not （Group B）. The two groups were compared for RLN injury and hypocalcaemia. Results： The numbers of patients and nerves at risk were 71 and 129 in Group A, and 63 and 121 in Group B, respectively, RLN injury in Group A （0） was significantly lower than that in Group B （5 [7.9%]） patients, 7 [5.8%] nerves） for the numbers of patients （P=0.016） and nerves at risk （P=0.006）. Temporary hypocalcaemia was significantly higher in Group A than in Group B （14 [24.1%] vs 6 [ 10.3%], P=0.049）, Permanent complications in Group B were significantly higher than those in Group A （13 [20.6%] vs 4 [5.6%], P=0.009）. Conclusion： RLN injury was prevented and permanent complications were decreased by identifying the whole course and branches of the recurrent laryngeal nerve during total thyroidectomy,     

Drainage after total thyroidectomy or lobectomy for benign thyroidal disorders

Objective： This prospective randomized clinical trial was conducted to evaluate the necessity of drainage after total thyroidectomy or lobectomy for benign thyroidal disorders. Methods： A total of 116 patients who underwent total thyroidectomy or lobectomy for benign thyroidal disorders were randomly allocated to be drained or not. Operative and postoperative outcomes including operating time, postoperative pain assessed by visual analogue scale （VAS）, total amount of intramuscular analgesic administration, hospital stay, complications, necessity for re-operation and satisfaction of patients were all assessed. Results： The mean operating time was similar between two groups （the drained and non-drained groups）. The mean VAS score was found to be significantly low in the non-drained group patients in postoperative day （POD） 0 and POD 1. The mean amount of intramuscular analgesic requirement was significantly less in the non-drained group. One case of hematoma, two cases ofseroma and three cases of transient hypoparathyroidism occurred in the non-drained group, whereas one case of hematoma, two cases of seroma, two cases of wound infections and two cases of transient hypoparathyroidism occurred in the drained group. No patient needed re-operation for any complication. The mean hospital stay was significantly shorter and the satisfaction of patients was superior in the non-drained group. Conclusion： These findings suggest that postoperative complications cannot be prevented by using drains after total thyroidectomy or lobectomy for benign thyroid disorders. Furthermore, the use of drains may increase postoperative pain and the analgesic requirement, and prolong the hospital stay. In the light of these findings, the routine use of drains might not be necessary after thyroid surgery for benign disorders.     

Vascular normalization in Rgs5-deficient tumours promotes immune destruction

The vasculature of solid tumours is morphologically aberrant and characterized by dilated and fragile vessels, intensive vessel sprouting and loss of hierarchical architecture. Constant vessel remodelling leads to spontaneous haemorrhages and increased interstitial fluid pressure in the tumour environment. Tumour-related angiogenesis supports tumour growth and is also a major obstacle for successful immune therapy as it prevents migration of immune effector cells into established tumour parenchyma. The molecular mechanisms for these angiogenic alterations are largely unknown. Here we identify regulator of G-protein signalling 5 (Rgs5) as a master gene responsible for the abnormal tumour vascular morphology in mice. Loss of Rgs5 results in pericyte maturation, vascular normalization and consequent marked reductions in tumour hypoxia and vessel leakiness. These vascular and intratumoral changes enhance influx of immune effector cells into tumour parenchyma and markedly prolong survival of tumour-bearing mice. This is the first demonstration, to our knowledge, of reduced tumour angiogenesis and improved immune therapeutic outcome on loss of a vascular gene function and establishes a previously unrecognized role of G-protein signalling in tumour angiogenesis.