Arrhythmogenesis in heart cells involves reverse E–C coupling and reverse electrotonic conduction along T-tubules

Early afterdepolarization (EAD) is an aberrant cardiac afterpotential that underlies the development of life-threatening ventricular arrhythmias. It is believed that the development of EAD is caused by the reactivation of L-type Ca2+ current during the period of the action potential plateau; however, the cellular mechanisms that underlie the development of EAD is still controversial. One favorable alternative is the depolarizing reverse-mode operation of the Na+/Ca2+ exchanger, which is activated by aberrant Ca2+ release from the sarcoplasmic reticulum in the process of reverse E–C coupling. Since EADs develop preferentially in damaged heart cells with abnormal Ca2+-signaling, here I studied the causal link between the development of EADs and aberrant intracellular Ca2+ level ([Ca2+]i) dynamics in mouse heart cells using the whole-cell clamp technique. My results show (1) the generation of EADs was preceded by the development of depolarizing membrane potential (Vm) fluctuation, (2) the depolarizing Vm fluctuation is associated with [Ca2+]i elevation, suggesting an involvement of reverse E–C coupling via the Na+/Ca2+ exchanger, and (3) that extending the T-tubules’ length constant by decreasing the extracellular K+ level facilitated the development of the Vm fluctuation and EADs. Taken together, I conclude that EADs are caused by the depolarizing Vm fluctuation, which is induced locally in the T-tubule membrane by aberrant [Ca2+]i elevation and is conducted back electrotonically along the T-tubules.

The effect of the obstacle on the hydraulic response of the composite hydraulic structure

Experimental investigations are carried out to study the physics of the flow that passes weir-gate hydraulic structure and encounters obstruction with or without installation of downstream opening. This study approaches the comparison between two different options; the first option deals with free flow condition while the second option deals with submerged flow condition. Various cases are performed considering different hydraulics variables and dimensions variables to evaluate the existence of obstruction with or without openings. Overall the flow pattern is more sensitive to the presence of obstruction at downstream region than in its absence. The hydraulic variables that are considered in the study are divided into dimensional variables such as discharge, downstream flow velocity and water depths at downstream and non-dimensional variables such as discharge coefficient, Froude number and Reynolds number. The obstacles which are used in this study have variable heights with constant width and length. Constant spacing between the obstacles is adopted. Different arrangements of obstacles are considered in this study and it is found that a significant and reasonable result is different among the cases. The effect of rectangular opening in the obstruction on flow pattern is studied. The effect of obstacles with rectangular opening gives a noticeable result in the assessment of the discharge coefficient of the composite hydraulic structure.

Breaking force analysis of cotton ring-spun yarns

The most important factor influencing the production efficiency of final textile products made from yarns as well as the product performance are the tensile properties of the yarn. The breaking force of spun yarns, assessed with standard static procedure, depends on several parameters, one of them being the testing conditions. In our research, the effect of testing conditions (climatic conditions, the ratio gauge length/constant rate of extension and sampling, which refers to the number of yarn package and the position of package winding, taken from the bobbin) on the breaking force of 100% cotton ring-spun yarns was analyzed using the statistical evaluation method “ANOVA”. The results clearly indicate that indeed all input parameters of testing conditions have a statistically significant effect on the breaking force of the yarn. When we judge the suitability of yarns to withstand a certain tension produced by technological procedures, not only average breaking force should be focused on. The information regarding the tested minimum breaking force of yarn becomes very important regarding our decision whether yarn fulfills the prescribed value of breaking force.

Competition brings out the best: modelling the frustration between curvature energy and chain stretching energy of lyotropic liquid crystals in bicontinuous cubic phases

It is commonly considered that the frustration between the curvature energy and the chain stretching energy plays an important role in the formation of lyotropic liquid crystals in bicontinuous cubic phases. Theoretic and numeric calculations were performed for two extreme cases: parallel surfaces eliminate the variance of the chain length; constant mean curvature surfaces eliminate the variance of the mean curvature. We have implemented a model with Brakke's Surface Evolver which allows a competition between the two variances. The result shows a compromise of the two limiting geometries. With data from real systems, we are able to recover the gyroid–diamond–primitive phase sequence which was observed in experiments.

Electrical Communication Within a Neuron

Postsynaptic potentials integrate across time and space within a single neuron. The influence of the length constant on spatial summation and of the time constant on temporal summation is described. Whereas passive properties give rise to graded potentials, the voltage-gated sodium channel (VGSC) supports the all-or-none action potential. The action potential can be used to conduct information across long distances and is therefore used in the majority of neurons that have axons. How the inactivated state of VGSCs gives rise to the refractory period and dynamic polarization is described. The meaning of the action potential threshold is fully considered and then applied to understand the clinical condition of hyperkalemic periodic paralysis. Trains of action potentials carry information, and degradation of the spike train compromises the message. The speed of action potential conduction along both unmyelinated and myelinated axons is explored. In closing, an overview of demyelinating diseases is offered.