Cavo-portal transposition in rat: a new simple model

Background  

Liver transplantation in presence of diffuse portal vein thrombosis is possible by using caval blood as portal inflow, through cavo-portal transposition. However, clinical results are heterogeneous and experimental studies are needed, but similar hemodynamic conditions are difficult to obtain, especially in small animals. Herein we describe a new simple model of cavo-portal transposition in rat.     

Semen analysis and seminal plasma biochemistry in two brothers with familial reciprocal translocation 46,XY,t(8;9)(p10;p10) transmitted by the father

Here we report familial balanced translocation (46,XY,t(8;9)(p10;p10) inherited by two brothers from the father. The first subject, 33 years old, was examined after 3 years of childless marriage. Semen analysis showed severe oligozoospermia, hypomotility and teratozoospermia. His brother, 29 years old, volunteered to join this study. He had not yet tried to start a family. Semen analysis showed dyspermia, but the condition was much less serious than his brother's. In both subjects, the secretory function of the epididymis and the genital tract accessory glands did not seem to be affected by this particular translocation. This case report highlights the importance of cytogenetic analysis in dealing with infertile patients suffering from severe dyspermia apparently sine causa. This is particularly the case when certain Assisted Reproductive Technology (ART) programs are recommended, where natural selection of the sperm no longer takes place (e.g. ICSI). The possible risk of an increase in fetal chromosomal abnormalities would suggest genetic counselling in all such situations.     

Mechanism of voltage sensing in Ca2+- and voltage-activated K+ (BK) channels

In neurosecretion, allosteric communication between voltage sensors and Ca²⁺ binding in BK channels is crucially involved in damping excitatory stimuli. Nevertheless, the voltage-sensing mechanism of BK channels is still under debate. Here, based on gating current measurements, we demonstrate that two arginines in the transmembrane segment S4 (R210 and R213) function as the BK gating charges. Significantly, the energy landscape of the gating particles is electrostatically tuned by a network of salt bridges contained in the voltage sensor domain (VSD). Molecular dynamics simulations and proton transport experiments in the hyperpolarization-activated R210H mutant suggest that the electric field drops off within a narrow septum whose boundaries are defined by the gating charges. Unlike Kv channels, the charge movement in BK appears to be limited to a small displacement of the guanidinium moieties of R210 and R213, without significant movement of the S4.

Excitable tissues accomplish their signaling functions thanks in part to the interplay of several voltage-sensitive ion channels (1–6). Hence, to understand these processes, it is crucial to establish how voltage-sensitive ion channels sense changes in the electric field across the membrane, an issue that has been a matter of extensive study and intense debate for decades. The most widely accepted mechanism proposes the existence of voltage-sensor domains (VSDs), modules that undergo two or more discrete conformational states in response to changes in the membrane voltage. The simplest model considers two states: active (A), which promotes pore opening, and resting (R), which promotes channel closing. To accomplish its function, VSDs contain voltage-sensitive particles, which move in response to changes in the electric field. This movement triggers the interconversion between the two discrete conformational states. These voltage-sensing particles are typically the guanidine groups of arginine residues within the S4 transmembrane segment, which undergo a combination of rotational, translational, and tilting movement in response to changes in membrane voltage (7–14).The large-conductance Ca²⁺- and voltage-activated K⁺ (BK) channels have a wide distribution in mammalian tissues (15–18), where they participate in a diversity of physiological processes. Their malfunction is often related to diverse pathological conditions (19, 20). BK channel open probability is independently regulated by membrane depolarization and intracellular Ca²⁺ concentration (21, 22), each stimulus being detected by specialized modules. Like other voltage-sensitive K⁺ (Kv) channels, BK is an homotetramer in which each of its α subunits consists of a pore domain (PD; S5-S6 transmembrane segments), a voltage-sensing domain (VSD; S1–S4 transmembrane segments) containing a positively charged S4, and a cytosolic C-terminal regulatory domain, which contains the Ca²⁺-binding sites (23, 24). Also, like some members of other K⁺ channel families (25, 26), the VSD and PD of BK are non–domain swapped (23, 24). BK channels display some distinctive structural and functional features: Despite sharing the selectivity filter sequence with Kv channels, BK unitary conductance and selectivity are exquisitely high (27–30). The BK α subunit has an additional transmembrane segment S0 [therefore, its N terminus faces the extracellular medium (31)], and the voltage sensitivity in BK channels is significantly lower than that of Kv channels, presumably because of their lower number of gating charges (32).Although thoroughly studied, research into BK VSD and its voltage dependence has faced several technical obstacles. The relatively small gating charge per channel (32) and the large conductance of the BK pore makes isolating of the gating currents from the ionic currents a tough experimental challenge. In addition, because mutations of VSD residues can produce very large shifts in both the gating charge-voltage (Q(V)) and the conductance-voltage G(V)) relationships (33), it is necessary to use extreme voltages to accurately measure the voltage dependence of some mutants. Consequently, the identification of BK gating charges has been addressed by using indirect approaches (33, 34). The combination of electrophysiology measurements and kinetic modeling suggests a decentralized VSD in the BK channel, where four charged residues (D153 and R167 in S2, D186 in S3, and R213 in S4) act as voltage sensor particles (33). A recent report of the atomistic cryo-electron microscopy (cryo-EM) structures of the human BK channel and its homolog in Aplysia californica (AcSlo) revealed minor structural differences between the VSD in both the Ca²⁺-bound (open pore) and the Ca²⁺-unbound (closed pore) conformations (23, 24, 35). This result can be explained if the conformational changes of the BK VSD upon activation are small compared to those that occur during the activation of other channels, such as HCN channels (12–14).In this study, we identified voltage-sensing particles in the BK channel by using a direct functional approach, involving gating of current measurements and analysis of the Q(V) curves spanning 800 mV in the voltage axis. Systematic neutralization of the individual charged residues in the VSD (S1–S4) revealed that only the neutralization of two arginines in S4 (R210 and R213) changed the voltage dependence of the Q(V) curves. Neutralization of other VSD charges point to roles in tuning of the half-activation voltage of the VSD and its allosteric coupling with the PD. Molecular dynamics (MD) simulations based on the cryo-EM structures of the human BK channel (35) as templates suggested that R210 and R213 lie in a very narrow septum separating intra- and extracellular water-filled vestibules. This interpretation is consistent with the robust hyperpolarization-activated proton currents generated when R210 is mutated to the protonable amino acid histidine. Overall, our results point to a unique and distinctive mode of activation in BK: In contrast to Kv channels, where positive charges move one by one through a charge transfer center (absent in BK channels) that spans the entire electric field (36, 37), charge movement in BK channels is limited to the small displacement of R210 and R213, which itself constitutes a narrow septum where the electric field drops.     

Incremental Value of Three‐Dimensional Echocardiography over the Two‐Dimensional Technique in the Assessment of Combined Sinus of Valsalva Rupture into the Right Ventricle and Adjacent Perimembranous Ventricular Septal Defect

We describe the incremental value of live/real time three‐dimensional (3D) echocardiography over the 2D technique in the assessment of ruptured right sinus of Valsalva into the right ventricle associated with an adjacent perimembranous ventricular septal defect in an elderly patient.     

Assessment of pulmonary toxicity of MgO nanoparticles in rats

In this study, we have evaluated the pulmonary toxicity of MgO nanoparticles (MgO NPs) in rats following their exposure. NPs in phosphate buffered saline + 1% Tween 80 were exposed via intratracheal instillation at a doses of 1 mg/kg or 5 mg/kg into rat lungs and evaluated for various tissue damage markers like alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) in bronchoalveolar lavage (BAL) fluid and histopathology of lungs at 1, 7, and 30 days of post‐exposure intervals. A dose‐dependant increase in ALP and LDH activity was observed in BAL fluids of rat lungs than sham control at all post‐exposure periods (P <0.05), and a dose‐dependant infiltration of interstitial lymphocytes, peribronchiolar lymphocytic infiltration, and dilated and/or congested vessels at 1 day post‐exposure period, worsened at 1 week period, and were reduced at 1 month at histology, indicating the pulmonary toxicity of MgO NPs. In conclusion, MgO NPs exposure produced a dose‐dependent pulmonary toxicity in rats and was comparable with that of Quartz particles. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 308–314, 2015.     

Safety of Lumbar Puncture Performed on Dual Antiplatelet Therapy

Practice guidelines generally recommend delaying lumbar puncture (LP) in patients on dual antiplatelet therapy, with these recommendations often citing an increased risk of hemorrhagic complications, specifically the development of epidural hematomas. However, no data exist about the risks of performing an LP in the setting of dual antiplatelet therapy and conclusions are often based on data from spinal anesthesia literature. We reviewed the medical records of 100 patients who underwent LP while taking dual antiplatelet therapy. We recorded the number of traumatic and bloody cerebrospinal fluid results as well as the presence of any complications occurring within 3 months of the procedure. Complications requiring imaging or hospitalization were considered serious. The most common complication was back pain, which was reported by 2 patients, only 1 of which was ultimately found to be attributable to the procedure. No serious complications occurred. Cerebrospinal fluid analysis was consistent with a traumatic LP, defined as having at least 100 red blood cells per microliter, in 8% of cases. Bloody LP, defined as having 1000 red blood cells per microliter, occurred in 4% of cases. The percentage of traumatic or bloody LPs was within the range reported previously for LPs performed in any setting. Although this is a small study and additional review is necessary, performing LPs in the setting of dual antiplatelet therapy may not pose an increased risk of serious complications.