Leukemia inhibitory factor-dependent increase in myoblast cell number is associated with phosphotidylinositol 3-kinase-mediated inhibition of apoptosis and not mitosis

Leukemia inhibitory factor (LIF) is an important regulator of skeletal muscle regeneration and has been suggested to be mitogenic for myogenic cells because it has been shown to increase the quantity of myoblast cells grown in culture over extended periods of time. Using the established C2C12 murine myoblast cell line, we observed that LIF treatment did not significantly increase the rate at which myoblasts synthesise DNA under conditions which increased cell quantity by 73% above control, whilst the known mitogen fibroblast growth factor-2 significantly increased DNA synthesis under these conditions. Consequently, we examined the capacity of LIF to prevent apoptotic cell death. LIF treatment significantly reduced staurosporine-induced apoptotic DNA fragmentation by 37% compared to control and also reduced the proteolytic activation of caspase-3 by 40% compared to control. This effect of LIF was completely abolished by addition of the phosphatidylinositol 3-kinase inhibitor wortmannin, indicating that the phosphatidylinositol 3-kinase signalling pathway, previously shown to be linked to LIF-dependent increases in cell number, is necessary in mediating the anti-apoptotic effects of LIF. LIF treatment was also associated with increased levels of Bcl-xL and XIAP transcripts compared to control. Therefore, we suggest that the role of LIF in skeletal muscle regeneration and myogenesis is that of a survival factor rather than a mitogen.

DefibViz: a visualization tool for the assessment of electrode parameters on transthoracic defibrillation thresholds

DefibViz is a software application developed for defibrillation simulation and visualization. It exploits both surface techniques and methods for the interactive exploration of volumetric datasets for the analysis of transthoracic defibrillation simulation results. DefibViz\ has a graphical user interface for the specification of the shape, size, position, and applied voltage of a defibrillator's electrodes. An option is provided for using 3-D slice plane widgets, which operate on the volumetric datasets, such that the distribution of the voltage gradient induced by an electric shock can be visually inspected in various tissues throughout the myocardium and torso. One goal of DefibViz is to enhance understanding of how electrode parameters relate to the change of the voltage gradient distribution throughout the heart, which may help lead to optimal defibrillator design. DefibViz; is significant, in that, it is built by using an open-source graphics and visualization framework providing a platform for subsequent modifiability and extensibility. Moreover, it integrates simulation and visualization techniques, which previously required the running of several independent software executables, into an enhanced, seamless, and comprehensive software application.

Finite element computer modeling of transthoracic atrial defibrillation

Placement of external electrodes can significantly affect the success rate of transthoracic atrial defibrillation, but studies have not led to agreement on optimal electrode placements. This study aims to (1) develop an anatomically realistic, finite element model of the human torso for external atrial defibrillation, (2) investigate model parameters of skeletal muscle conductivity and anisotropy and the presence of subcutaneous fat, and (3) investigate clinical defibrillation parameters of electrode size, shape, and location. The model predicts atrial defibrillation threshold (ADFT) energy by requiring a voltage gradient of 5 V/cm over at least 95% of atrial myocardium. The model compares favorably with a clinical study of 301 patients that reported an anterior-posterior electrode position required approximately 20% less energy than an anterior-anterior position. Results indicate that a change in electrode size has a different effect for different electrode placements. This study finds that variation in electrode placement by only a few centimeters can change ADFTs by up to 51%. This is the first computer model of transthoracic atrial defibrillation to our knowledge. Our computer model is not limited to a few empirically selected electrode placements as in clinical studies and can test any location, size, and number of electrode placements.