Determination of coumarin in seasonal bakery products using QuEChERS and GC-MS.

Cinnamon is a traditional herbal drug, but more importantly, it is used as a flavor compound in the production of foodstuff. Due to the content of significant concentrations of coumarin in Cassia cinnamon, effective control of the coumarin content in seasonal bakery products like ginger bread and cinnamon biscuits is urgently needed. Here we present a novel, fast and fully validated protocol for the determination of coumarin in marketed bakery products using the QuEChERS sample preparation technique in combination with GC-MS analysis. Ten grams of homogenized sample was mixed with 20 mL acetonitrile/water (1:1) and 5 g magnesium sulfate/sodium chloride mixture (4:1). The organic phase was cleaned by dSPE with 25 mg magnesium sulfate/PSA (5:1). The LOD was 0.15 µg/mL and the LOQ 0.50 µg/mL. We detected a mean coumarin content of 19.5 µg/kg in 9 out of 14 seasonal food products (ranging from 1.45 to 39.4 mg/kg). No coumarin was detected in five cinnamon containing products. With this investigation we demonstrate that the QuEChERS sample preparation, previously applied mainly to the analysis of pesticides in vegetables, is also suitable for other complex matrices.

Analysis of cefaclor in novel chocolate-based camouflage capsules.

The determination of cefaclor in a new, complex chocolate matrix was performed by using a simple sample preparation (dispersion in dilute hydrochloric acid at 80 degrees C, centrifugation, washing with cyclohexane), followed by ion pair HPLC on a Kinetex pentafluorophenyl core-shell stationary phase with UV detection at 265 nm. We obtained good linearity (R2 = 0.9976) and precision (average RSD 0.86%) for the relevant concentration range. The preparations, although hand-made in this pilot phase, showed good uniformity of content. After being stored for four weeks in a refrigerator the preparation did not contain recognizable amounts of decomposition products.

Action potential characteristics and arrhythmogenic properties of the cardiac conduction system of the murine heart.

Studies have characterized conduction velocity in the right and left bundle branches (RBB, LBB) of normal and genetically engineered mice. However, no information is available on the action potential characteristics of the specialized conduction system (SCS). We have used microelectrode techniques to characterize action potential properties of the murine SCS, as well as epicardial and endocardial muscle preparations for comparison. In the RBB, action potential duration at 50%, 70%, and 90% repolarization (APD(50,70,90)) was 6+/-0.7, 35+/-6, and 90+/-7 ms, respectively. Maximum upstroke velocity (dV/dt(max)) was 153+/-14 V/s, and conduction velocity averaged 0.85+/-0.2 m/s. APD(90) was longer in the Purkinje network of fibers (web) than in the RBB (P<0.01). Web APD(50) was longer in the left than in the right ventricle (P<0.05). Yet, web APD(90) was longer in the right than in the left ventricle (P<0.001). APD(50,70) was significantly longer in the endocardial than in the epicardial (P<0.001; P<0.003). APD(90) in the epicardial and endocardial was shorter than in the RBB ( approximately 36 ms versus approximately 100 ms). Spontaneous electrical oscillations in phase 2 of the SCS occasionally resulted in early afterdepolarizations. These results demonstrate that APDs in the murine SCS are significantly ( approximately 2-fold) longer than in the myocardium and implicate the role of the murine SCS in arrhythmias. The differences should have important implications in the use of the mouse heart to study excitation, propagation, and arrhythmias.

Mechanoelectric feedback in a model of the passively inflated left ventricle.

Mechanoelectric feedback has been described in isolated cells and intact ventricular myocardium, but the mechanical stimulus that governs mechanosensitive channel activity in intact tissue is unknown. To study the interaction of myocardial mechanics and electrophysiology in multiple dimensions, we used a finite element model of the rabbit ventricles to simulate electrical propagation through passively loaded myocardium. Electrical propagation was simulated using the collocation-Galerkin finite element method. A stretch-dependent current was added in parallel to the ionic currents in the Beeler-Reuter ventricular action potential model. We investigated different mechanical coupling parameters to simulate stretch-dependent conductance modulated by either fiber strain, cross-fiber strain, or a combination of the two. In response to pressure loading, the conductance model governed by fiber strain alone reproduced the epicardial decrease in action potential amplitude as observed in experimental preparations of the passively loaded rabbit heart. The model governed by only cross-fiber strain reproduced the transmural gradient in action potential amplitude as observed in working canine heart experiments, but failed to predict a sufficient decrease in amplitude at the epicardium. Only the model governed by both fiber and cross-fiber strain reproduced the epicardial and transmural changes in action potential amplitude similar to experimental observations. In addition, dispersion of action potential duration nearly doubled with the same model. These results suggest that changes in action potential characteristics may be due not only to length changes along the long axis direction of the myofiber, but also due to deformation in the plane transverse to the fiber axis. The model provides a framework for investigating how cellular biophysics affect the function of the intact ventricles.

Three-dimensional stress and strain in passive rabbit left ventricle: a model study.

To determine regional stress and strain distributions in rabbit ventricular myocardium, an anatomically detailed finite element model was used to solve the equations of stress equilibrium during passive filling of the left ventricle. Computations were conducted on a scalable parallel processing computer and performance was found to scale well with the number of processors used, so that stimulations previously requiring approximately 60 min were completed in just over 5 min. Epicardial strains from the model analysis showed good agreement (RMSE = 0.007332) with experimental measurements when material properties were chosen such that cross fiber strain was more heterogeneous than fiber strain, which is also consistent with experimental observations in other species.

Three-dimensional analysis of regional cardiac function: a model of rabbit ventricular anatomy.

The three-dimensional geometry and anisotropic properties of the heart give rise to nonhomogeneous distributions of stress, strain, electrical activation and repolarization. In this article we review the ventricular geometry and myofiber architecture of the heart, and the experimental and modeling studies of three-dimensional cardiac mechanics and electrophysiology. The development of a three-dimensional finite element model of the rabbit ventricular geometry and fiber architecture is described in detail. Finally, we review the experimental results, from the level of the cell to the intact organ, which motivate the development of coupled three-dimensional models of cardiac electromechanics and mechanoelectric feedback.