Like many of the established animal based

Like many of the established animal based ex vivo cardiac safety pharmacology models (Langendorf, Purkinje fiber, ventricular wedge) the present assay is based on measuring the net cellular electrical activity (monophasic statins hmg coa reductase inhibitors or field potential in case of the MEA) instead of a single isolated current. The action potential relies on the interaction and relative contribution of many ion channels, which is subject to considerable species differences (Nerbonne and Kass, 2005; Terrar et al., 2006). Therefore it is of interest to work with human cells. Taking the full property spectrum of cardiomyocytes into account is an obvious advantage; however it also results in an additional complexity. Some compounds might show no effect because the net effect on cardiac repolarization is zero (for example in case of dual calcium and hERG block) while others might show variable effects due to multi-channel block. The last point is illustrated by increasing variability in the micro-molar range of most compounds. One-way ANOVA and Bonferroni\'s multiple comparison post-tests indicate that the 30μM data-point gives significant more variation than the three lowest concentrations in the single drug experiments (p<0,05). Finally, some compound effects may be masked by the functionality of other ion channels. An example of this was our failure to find major effects with IKs blocking drugs. However a simple challenge with either d,l-sotalol or dofetilide reduced the repolarization reserve and exposed the effects of IKs blockers. Interestingly, we observed that although all combinations of IKr and IKs blockers and IKs blockers on LQTS2 cells yield similar results, it is evident that the pharmacological experiments with dofetelide and IKs blockers yield more pronounced FPD prolongations compared either d,l-sotalol and IKs block or LQTS2 cells and IKs block. The concentration of d,l-sotalol used in these experiments is in the estimated therapeutic plasma concentration unbound range (ETPCunbound) (Supplemental Table 2) while the concentration of Dofetelide used in this experiment is approximately 15× higher than the ETPCunbound. This might explain the difference between d,l-sotalol and dofetelide in Fig. 3. Since the ETPCunbound will not be known early in compound development it is of interest to profile unknown compounds under various controlled conditions (e.g. in spontaneously beating control cells and in conditions mimicking reduced repolarization reserve). Traditional patch clamp electrophysiology techniques may subsequently be used if the stem cell based field potential duration assay suggests unwanted side effects on cardiac repolarization. Eventually structure activity relationships may then be used to develop analogues with reduced side effects.
Acknowledgments
Introduction Neural progenitor-based therapies are rapidly emerging as a potential strategy for central nervous system (CNS) regeneration in patients with neurodegenerative diseases or injury. The aim of this therapy is to replace, repair, or enhance the biological functions of damaged tissues. However, neural progenitors availability, immune reaction and ethical concerns are limitations for its medical application. The skeletal muscle, as one of the largest organs in the body, represents an alternative source of stem cells, which can be easily obtained in large quantities through a biopsy procedure performed in an outpatient clinic (Wu et al., 2010). Thus, the skeletal muscle may be a convenient and enriched source of neural cells that may circumvent these limitations. Previously, we isolated Nestin–GFP+ cells in cultured adult skeletal muscle from Nestin–GFP transgenic mice, which exhibit characteristics of neural progenitors such as morphology, specific neural markers profile, replicative capacity, ability to form neurospheres, and functional response to neurotransmitter (Birbrair et al., 2011; Birbrair et al., in press). Our laboratory is working to determine whether these cells form functional neurons in the brain.