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The L-Type calcium channel (LTCC) is a heteromultimeric protein complex with an important function in cardiac biology since it ensures the main entry path for calcium into the cardiomyocytes. Its conductance increases during membrane depolarization, whereas decreases during calcium- and voltage-dependent inactivation. In addition, G protein-coupled receptor (GPCR) signaling provides a further regulatory layer for fine-tuning the LTCC (Catterall, 2000; van der Heyden et al., 2005). The α1C subunit is the main pore forming subunit of the LTCC, which is expressed at high levels in cardiomyocytes and is encoded by the CACNA1C gene (Weiss et al., 2013). It comprises of a cytosolic N- and C-terminal tails and four transmembrane domains, which harbor the ion-selective pore, voltage sensor and gating machinery (Carafoli et al., 2001). Its C-terminal tail (CT) serves as a scaffold for channel modulating molecules downstream of the GPCR signaling, including kinases and phosphatases (Catterall, 2000). Over the past few decades the LTCC regulation via β-AR/Gs protein systems was well demonstrated. However, little attention has been paid to its regulation via alternative GPCR-like systems such as Wnt11/Calcium pathway (Panáková et al., 2010). The present study provides evidence that Wnt11 signaling regulates the LTCC, hence the electrical gradient formation in developing zebrafish heart. I showed that loss of WNT11 induces the generation of a CT isoform in A-kinase anchoring protein (AKAP) anchored Protein kinase A (PKA) signaling dependent manner. Systematic analysis of all the AKAP candidates revealed that PKA targeting through AKAP2 to the CT plays a pivotal role in this isoform formation. In developing zebrafish heart Akap2 is indispensable for the proper heart looping and regulates the LTCC localization and abundance. In cooperation with the Wnt11 pathway it establishes the electrical gradient formation, since loss of akap2 rescued the abnormal cell coupling in wnt11-deficient hearts. These findings provide evidence that Wnt11 signaling compartmentalizes LTCC conductance by targeting PKA/AKAP2 required for the proper formation of intercellular cell coupling., Der L-Typ-Calciumkanal (LTCC) ist ein heteromultimerer Proteinkomplex mit einer wichtigen Funktion in der kardiovaskulären Biologie, da dieser die hauptsächliche Eintrittsmöglichkeit von Calcium in Herzmuskelzellen sicherstellt. Die Leitfähigkeit des LTCC steigt während der Membrandepolarisation und sinkt während der Calcium- oder Spannungsabhängigen Inaktivierung. Darüber hinaus stellt der G Protein-gekoppelte Rezeptor (GPCR) Signalweg eine weitere regulatorische Ebene zur Feinjustierung des LTCC dar (Catterall, 2000; M. a G. van der Heyden, Wijnhoven, & Opthof, 2005). Die α1C Untereinheit ist hauptursächlich für die Porenbildung des LTCC, wird in großen Mengen in Herzmuskelzellen exprimiert und vom CACNA1C Gen kodiert (Weiss et al., 2013). Die α1C Untereinheit umfasst einen zytosolischen N- und C-terminalen Schwanz und vier Transmembrandomänen, welche die ionenselektive Pore, den Spannungssensor und die Gating-Maschinerie beherbergen (Carafoli et al., 2001). Sein C-terminaler Schwanz (CT) dient als Gerüst für kanalmodulierende Moleküle stromabwärts des GPCR-Signalwegs, einschließlich Kinasen und Phosphatasen (Catterall, 2000). In den letzten Jahren wurde die Regulation des LTCC durch das β-AR/Gs Proteinsystem ausführlich bewiesen. Jedoch ist der Regulation durch das alternative GPCR-ähnliche System, wie dem Wnt11/Calcium Signalweg, dabei wenig Aufmerksamkeit zugekommen (Panáková et al., 2010). Die vorliegende Studie erbringt Nachweise, dass der Wnt11-Signalweg den LTCC reguliert, und damit einhergehend die elektrische Gradientenbildung im sich entwickelnden Zebrafisch Herz. Ich habe gezeigt, dass der Verlust von WNT11 zur Erzeugung einer CT Isoform führt, abhänging von der A-Kinase Ankerprotein (AKAP)-verankerte Protein Kinase A (PKA)-Signalgebung. Eine systematische Analyse aller AKAP-Kandidaten ergab, dass PKA über AKAP2 auf den CT abzielt und so eine entscheidende Rolle bei der Bildung dieser Isoform spielt. Im sich entwickelnden Zebrafischherzen ist Akap2 unentbehrlich für das Looping des Herzens und reguliert die Lokalisation sowie Häufigkeit des LTCC. Zusammen mit dem Wnt11-Signalweg wird die elektrische Gradientenbildung etabliert, da der Verlust von akap2 die abweichende Zellkopplung in wnt11-defizienten Herzen wiederherstellt. Diese Erkenntnisse erbringen den Beweis dafür, dass der Wnt11-Signalweg die Leitfähigkeit des LTCC kompartmentalisiert, indem er auf die AKAP2/PKA-Interaktion abzielt, welche für die korrekte Bildung der interzellulären Kopplung benötigt wird.

Genetic factors may be learnt from families with gene mutations that render nerve-injury susceptibility even to ordinary physical activities. A typical example is hereditary neuropathy with liability to pressure palsies (HNPP). HNPP is caused by a heterozygous deletion of PMP22 gene. PMP22 deficiency disrupts myelin junctions (such as tight junction and adherens junctions), leading to abnormally increased myelin permeability that explains the nerve susceptibility to injury. This finding should motivate investigators to identify additional genetic factors contributing to nerve vulnerability of injury.

A characteristic histological feature of striated muscle cells is the presence of deep invaginations of the plasma membrane (sarcolemma), most commonly referred to as T-tubules or the transverse-axial tubular system (TATS). TATS mediates the rapid spread of the electrical signal (action potential) to the cell core triggering Ca(2+) release from the sarcoplasmic reticulum, ultimately inducing myofilament contraction (excitation-contraction coupling). T-tubules, first described in vertebrate skeletal muscle cells, have also been recognized for a long time in mammalian cardiac ventricular myocytes, with a structure and a function that in recent years have been shown to be far more complex and pivotal for cardiac function than initially thought. Renewed interest in T-tubule function stems from the loss and disorganization of T-tubules found in a number of pathological conditions including human heart failure (HF) and dilated and hypertrophic cardiomyopathies, as well as in animal models of HF, chronic ischemia and atrial fibrillation. Disease-related remodeling of the TATS leads to asynchronous and inhomogeneous Ca(2+)-release, due to the presence of orphan ryanodine receptors that have lost their coupling with the dihydropyridine receptors and are either not activated or activated with a delay. Here, we review the physiology of the TATS, focusing first on the relationship between function and structure, and then describing T-tubular remodeling and its reversal in disease settings and following effective therapeutic approaches.

Fibrotic myocardial remodeling is typically accompanied by the appearance of myofibroblasts (MFBs). In vitro, MFBs were shown to slow conduction and precipitate ectopic activity following gap junctional coupling to cardiomyocytes (CMCs). To gain further mechanistic insights into this arrhythmogenic MFB-CMC crosstalk, we performed numerical simulations in cell-based high-resolution two-dimensional tissue models that replicated experimental conditions. Cell dimensions were determined using confocal microscopy of single and co-cultured neonatal rat ventricular CMCs and MFBs. Conduction was investigated as a function of MFB density in three distinct cellular tissue architectures: CMC strands with endogenous MFBs, CMC strands with coating MFBs of two different sizes, and CMC strands with MFB inserts. Simulations were performed to identify individual contributions of heterocellular gap junctional coupling and of the specific electrical phenotype of MFBs. With increasing MFB density, both endogenous and coating MFBs slowed conduction. At MFB densities of 5–30%, conduction slowing was most pronounced in strands with endogenous MFBs due to the MFB-dependent increase in axial resistance. At MFB densities >40%, very slow conduction and spontaneous activity was primarily due to MFB-induced CMC depolarization. Coating MFBs caused non-uniformities of resting membrane potential, which were more prominent with large than with small MFBs. In simulations of MFB inserts connecting two CMC strands, conduction delays increased with increasing insert lengths and block appeared for inserts >1.2 mm. Thus, electrophysiological properties of engineered CMC-MFB co-cultures depend on MFB density, MFB size and their specific positioning in respect to CMCs. These factors may influence conduction characteristics in the heterocellular myocardium.

Continuing to discover how the brain works is one of the great challenges ahead of us. Although understanding the brain anatomy and its functional organization provided a first and indispensable foundation, it became clear that a static view was insufficient. To understand the complexity of neuronal communication, it is necessary to examine the chemical nature of the neurotransmission and, using the example of the acetylcholine receptors, follow the different layers of networks that can be distinguished. The natural alkaloid nicotine contained in tobacco leaves acts as an agonist with a subclass of acetylcholine receptors, and provides an interesting tool to approach brain functions. Analysis of the nicotinic acetylcholine receptors, which are ligand gated channels, revealed that these receptors are expressed at different critical locations on the neurons including the synaptic boutons, neurites, cell bodies, and even on the axons. These receptors can modulate the activity at the microcircuit synaptic level, in the cell processing of information, and, by acting on the velocity of action potential, the synchrony of communication between brain areas. These actions at multiple levels of brain organization provide an example of the complexity of brain neurocircuitry and an illustration of the relevance of this knowledge for psychiatry.

The efficient propagation of action potentials along nervous fibers is necessary for animals to interact with the environment with timeliness and precision. Myelination of axons is an essential step to ensure fast action potential propagation by saltatory conduction, a process that requires highly concentrated voltage-gated sodium channels at the nodes of Ranvier. Recent studies suggest that the clustering of sodium channels can influence axonal impulse conduction in both myelinated and unmyelinated fibers, which could have major implications in disease, particularly demyelinating pathology. This comprehensive review summarizes the mechanisms governing the clustering of sodium channels at the peripheral and central nervous system nodes and the specific roles of their clustering in influencing action potential conduction. We further highlight the classical biophysical parameters implicated in conduction timing, followed by a detailed discussion on how sodium channel clustering along unmyelinated axons can impact axonal impulse conduction in both physiological and pathological contexts.

Cardiac muscle is a syncytial tissue of electrically coupled cells in which excitation of one cardiomyocyte spreads to all cardiomyocytes. Mechanisms of cell coupling in myocardial tissue can be categorized in two main groups: mechanisms that connect the intracellular parts of myocytes together (i.e., gap junctions), and mechanisms that act through changes in the small extracellular space of intercalated disks (ICD). The latter mechanisms are electric field coupling, ephaptic coupling, K accumulation, and capacitive coupling (Sperelakis and McConnell, 2002). ICD cleft has a limited space and therefore a small ionic current can change both its electric and diffusion potentials via the change in the ionic concentration. The potassium accumulation, for instance, can change the reversal potential of potassium channels toward more positive values, and as a results of which the potassium current can depolarize the cells. When ionic currents change the electric potential of cleft we have ephaptic or electrical coupling, and when the capacitive current of membrane changes the electric potential we have capacitive coupling. In electrical coupling through gap junctions, both experimental and modeling studies show that the reduction of propagation velocity is proportional to the reduction of gap junction density or conductance. In the case of coupling through ICD field potential, since the experimental data are based on the effect of these mechanisms on conduction velocity (not a direct measurement of the field potential), there are significant discrepancies between different experiments, and between experiments and simulation studies (Rhett et al., 2013). One explanation of these differences is to consider a mixture of excitatory and inhibitory effects for each of these mechanisms and suppose that each experiment grasp one feature of these mechanisms based on the experimental condition. Such a mixed behavior was proposed for the ephaptic coupling in a previous study, where the voltage gated sodium channels of the ICD negatively impacted the conduction velocity unless more than 10% of the gap junctions remained active. Further reduction of gap junction density was reversed their impact (Kucera et al., 2002). In the case of capacitive coupling, also, we suggest that a mixture of excitatory and inhibitory effects take place; so that depending on the compartment on which the membrane potential is measured, different effects may be observed. In capacitive coupling, we have two capacitors that share a voltage node, but each end of these capacitors are connected to different intracellular voltage nodes that provide the main polarity of the capacitors. Since these capacitors have a different polarity (Figure ​(Figure1A),1A), discharge (depolarization) of one of them by action potential generation would charge (hyperpolarize) the other one. Still, these capacitors in series can pass the current, which would increase the potential in the next intracellular voltage node. The hyperpolarization of ICD membrane was reported in a previous modeling study, but due to the complex nature of their model it was impossible to dissociate the electrical field coupling from the capacitive coupling (Ge and Sperelakis, 1992). Figure 1 Capacitive coupling simulation. (A) The equivalent circuit of intercalated disk. (B) Cell arrangement in the final model. Colors show the membrane potential in all cells. (C) Membrane potential and extracellular voltage in different locations of the intercalated ... We have simulated ICD in the NEURON simulation environment (Hines and Carnevale, 1997). In our model, an equivalent circuit of the ICD connects 10 myocytes together in the ICD (Figure ​(Figure1B).1B). Our model could potentially simulate ion channels in the cleft and gap junction. Capacitive coupling is the property of membranes lacking ion channels. Therefore, in the Figure ​Figure1C,1C, we show results of this model where there is no gap junction and ion channels in the ICD. The results of this model clearly show that the capacitive coupling hyperpolarizes the neighboring membrane in the ICD and depolarizes the adjacent myocyte membrane to some extent. Overall, based on the abovementioned simulation we hypothesize that the capacitive coupling has mixed excitatory and inhibitory effects. Therefore, we suggest that action potential propagation models should be revised based on this finding.

Computer modeling has played a unique role in understanding electrocardiography. Modeling and simulating cardiac action potential propagation is suitable for studying normal and pathological cardiac activation. This paper presents a 2-D Cellular Automata model for simulating action potential propagation in cardiac tissue. We demonstrate a novel algorithm in order to use minimum neighbors. This algorithm uses the summation of the excitability attributes of excited neighboring cells. We try to eliminate flat edges in the result patterns by inserting probability to the model. We also preserve the real shape of action potential by using linear curve fitting of one well known electrophysiological model., {"references":["N. Menke, M.D.; S. Angus; K. Cooper, V. Shah, \"A Simple 2-D Model\nof Cardiac Tissue Conduction\"","M. C. Trudel, R. M. Gulrajani, L. J. Leon, \"simulation of propagation in\na realistic-geometry computer heart model with parallel processing\"","C. R. H. Barbosa, \"Simulation of a plane wavefront propagating in\ncardiac tissue using a cellular automata model\", Phys. Med. Biol. 48,\n4151-4164.","P. B. Gharpure, C.r R. Johnson, \"A Cellular Automaton Model of\nElectrical Activation in Canine Ventricles: A Validation Study,\" SCI\nINSTITUTE, 1995.","C. L. Chang, Y., Zhang, Y. Y. Gdong, \"Cellular Automata For Edge\nDetection Of Images\", Proceedmgs of the Third Intetnauonal Conference\non Machine Learning and Cybernetics, Shanghai, 26-29 August 2004.","Z. Li-Sheng, \"Cellular Automaton Simulations for Target Waves in\nExcitable Media\", Commun. Theor. Phys. (Beijing, China), Vol. 53, No.\n1, pp. 171-174, January 15, 2010.","W. E. S. Yu, R. P. Saldana, \"Computational Aspects of Modeling\nExcitable Media Using Cellular Automata\"","D. Makowiec, \"cellular automata model of cardiac pacemaker\"","E. Costa Monteiro, L. C. Miranda, A. C. Bruno, and P. Costa Ribeiro,\n\"A Cellular Automaton Computer model for the study of magnetic\ndetection of cardiac tissue activation during artial flutter,\" IEEE\ntransaction on magnetics, Vol. 34, NO. 5, Sep. 1998.\n[10] K. M. Moe, C.R. Werner, J.A. Abildson, N.Y. Utica, \"A computer\nmodel of atrial fibrillation,\" American Heart Journal, Vol 67, pp 200-\n220, 1964.\n[11] M. Gerhardt, H. Schuster, J.J Tyson, \"A cellular automation model of\nexcitable media including curvature and dispersion,\" Science, Vol 247,\npp 1563-1566, 1990.\n[12] M. Markus, B. Hess, \"Isotropic cellular automaton for modelling\nexcitable media,\" Nature, Vol 347, pp 56-58, 1990.\n[13] J.R Weimar, J.J Tyson, L.T Watson, \"Diffusion and wave propagation\nin cellular automaton models of excitable media,\" Physica D, Vol 55, pp\n309-327, 1992.\n[14] J.R Weimar, J.J Tyson, L.T Watson, \"Third generation Cellular\nAutomaton for Modeling Excitable Media,\" Physica D, Vol 55, pp 328-\n339, 1992.\n[15] http://cor.physiol.ox.ac.uk/\n[16] www.ocp.ltd.uk/ap1.html"]}

In the present study, we tested the hypothesis that similar to other mechanical loads, notably cyclic stretch (simulating pre-load), glass microspheres simulating afterload will stimulate the secretion of angiogenic factors. Hence, we employed glass microspheres (average diameter 15.7 microm, average mass 5.2 ng) as a new method for imposing mechanical load on neonatal rat ventricular myocytes (NRVM) in culture. The collagen-coated microspheres were spread over the cultures at an estimated density of 3000 microspheres/mm2, they adhered strongly to the myocytes, and acted as small weights carried by the cells during their contraction. NRVM were exposed to either glass microspheres or to cyclic stretch, and several key angiogenic factors were measured by RT-PCR. The major findings were: (1) In contrast to other mechanical loads, such as cyclic stretch, microspheres (at 24 hrs) did not cause hypertrophy. (2) Further, in contrast to cyclic stretch, glass microspheres did not affect Cx43 expression, or the conduction velocity measured by means of the Micro-Electrode-Array system. (3) At 24 hrs, glass microspheres caused arrhythmias, probably resulting from early afterdepolarizations. (4) Glass microspheres caused the release of angiogenic factors as indicated by an increase in mRNA levels of vascular endothelial growth factor (80%), angiopoietin-2 (60%), transforming growth factor-beta (40%) and basic fibroblast growth factor (15%); these effects were comparable to those of cyclic stretch. (5) As compared with control cultures, conditioned media from cultures exposed to microspheres increased endothelial cell migration by 15% (P0.05) and endothelial cell tube formation by 120% (P0.05), both common assays for angiogenesis. In conclusion, based on these findings we propose that loading cardiomyocytes with glass microspheres may serve as a new in vitro model for investigating the role of mechanical forces in angiogenesis and arrhythmias.