A1152D mutation of the Na+ channel causes paramyotonia congenita and emphasizes the role of DIII/S4–S5 linker in fast inactivation

Missense mutations in the human skeletal muscle Na⁺ channel α subunit (hSkM1) are responsible for a number of muscle excitability disorders. Among them, paramyotonia congenita (PC) is characterized by episodes of muscle stiffness induced by cold and aggravated by exercise. We have identified a new PC-associated mutation, which substitutes aspartic acid for a conserved alanine in the S4–S5 linker of domain III (A1152D). This residue is of particular interest since its homologue in the rat brain type II Na⁺ channel has been suggested as an essential receptor site for the fast inactivation particle. To identify the biophysical changes induced by the A1152D mutation, we stably expressed hSkM1 mutant or wild-type (WT) channels in HEK293 (human embryonic kidney) cells, and recorded whole-cell Na⁺ currents with the patch-clamp technique. Experiments were performed both at 21 and 11°C to better understand the sensitivity to cold of paramyotonia. The A1152D mutation disrupted channel fast inactivation. In comparison to the WT, mutant channels inactivated with slower kinetics and displayed a 5 mV depolarizing shift in the voltage dependence of the steady-state. The other noticeable defect of A1152D mutant channels was an accelerated rate of deactivation from the inactivated state. Decreasing temperature by 10°C amplified the differences in channel gating kinetics between mutant and WT, and unveiled differences in both the sustained current and channel deactivation from the open state. Overall, cold-exacerbated mutant defects may result in a sufficient excess of Na⁺ influx to produce repetitive firing and myotonia. In the light of previous reports, our data point to functional as well as phenotypic differences between mutations of conserved S4–S5 residues in domains II and III of the human skeletal muscle Na⁺ channel.     

Thoracic surgery in United Arab Emirates

The United Arab Emirates (UAE) has undergone a significant change in its population and economy in the last decades and in parallel its healthcare system has evolved rapidly to provide advanced, innovative and world-leading care. At the forefront of this revolution in healthcare is the development of a multidisciplinary multimodality thoracic service provision, offered at quaternary referral hospitals amalgamating academics, training, research and innovation. Previously, thoracic service care was limited to single providers at various public and private hospitals, usually performing lower complexity cases. Most complex thoracic cases were repatriated outside the UAE. This practice was replaced with the opening of Cleveland Clinic Abu Dhabi (CCAD), in 2015, which created a multidisciplinary thoracic program. This included the start of a mini-invasive surgical and lung transplantation program. Since that time other public and private hospitals have emerged providing care in a similar model. The impact of these programs has been a decreased transfer of patients abroad for treatment. Under the umbrella of the Emirates Thoracic Society (ETS) a platform for greater collaboration aimed at improving patient care, potential research and physician education has been created. Direct links have been established with world-leading Thoracic surgery and Respiratory Medicine Centers facilitating this development and offering support and guidance. This article charts these changes in thoracic care in the recent past, present, and delineates plans for the future in the UAE.     

Cardiovascular and metabolic responses to catecholamine and sepsis prognosis: a ubiquitous phenomenon?

Many parameters have been associated with sepsis prognosis. In the present issue of Critical Care, Kumar and colleagues demonstrate that a preserved cardiac answer to dobutamine evaluated by radionucleotide measurements was associated with a better prognosis during septic shock. In this context, it is interesting to note that not only is the cardiac response to catecholamine stimulation associated with prognosis, but also the vascular and metabolic responses are associated. The ability of exogenous catecholamine to increase the arterial pressure (dopamine test) or to increase the lactate level is also related to prognosis. According to the ubiquitous character of catecholamine sensitivity, therefore, we should think in terms of cellular ability to respond to catecholamines in defining the concept of physiological reserve.     

Comparative effects of recombinant human activated protein C and dexamethasone in experimental septic shock

Purpose  

To compare the effects of recombinant human activated protein C (APC) and glucocorticoids alone and in combination in non-anesthetized resuscitated septic shock induced by cecal ligation and puncture (CLP) on (a) survival, (b) hemodynamics, and (c) vascular reactivity. The effects of treatments on major cellular pathways likely implicated were also studied.     

Cold extends electromyography distinction between ion channel mutations causing myotonia

OBJECTIVE: Myotonias are inherited disorders of the skeletal muscle excitability. Nondystrophic forms are caused by mutations in genes coding for the muscle chloride or sodium channel. Myotonia is either relieved or worsened by repeated exercise and can merge into flaccid weakness during exposure to cold, according to causal mutations. We designed an easy electromyography (EMG) protocol combining repeated short exercise and cold as provocative tests to discriminate groups of mutations. METHODS: Surface-recorded compound muscle action potential was used to monitor muscle electrical activity. The protocol was applied on 31 unaffected control subjects and on a large population of 54 patients with chloride or sodium channel mutations known to cause the different forms of myotonia. RESULTS: In patients, repeated short exercise test at room temperature disclosed three distinct abnormal patterns of compound muscle action potential changes (I-III), which matched the clinical symptoms. Combining repeated exercise with cold exposure clarified the EMG patterns in a way that enabled a clear correlation between the electrophysiological and genetic defects. INTERPRETATION: We hypothesize that segregation of mutations into the different EMG patterns depended on the underlying pathophysiological mechanisms. Results allow us to suggest EMG guidelines for the molecular diagnosis, which can be used in clinical practice.     

Vascular ATP-sensitive potassium channels are over-expressed and partially regulated by nitric oxide in experimental septic shock

Purpose  

To study the activation and expression of vascular (aorta and small mesenteric arteries) potassium channels during septic shock with or without modulation of the NO pathway.     

Isomeric N,N-bis(cyclohexanol)amine aryl esters: the discovery of a new class of highly potent P-glycoprotein (Pgp)-dependent multidrug resistance (MDR) inhibitors

A new series of P-glycoprotein (Pgp)-dependent multidrug resistance (MDR) inhibitors having a N,N-bis(cyclohexanol)amine scaffold have been designed, following the frozen analog approach. With respect to the parent flexible molecules, the new compounds show improved potency and efficacy. Among them, compound 1d, on anthracycline-resistant erythroleukemia K562 cells, is able to completely reverse Pgp-dependent MDR at low nanomolar concentration.