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The mechanisms responsible for atrial fibrillation (AF) are complex. At the tissue and cellular level, Ca2+ currents are down-regulated whereas repolarizing K+ currents are maintained, leading to action potential shortening. At the protein level however, Kv1.5 channels, the molecular expression of IKur, the main repolarizing current in human atria, is significantly decreased. We used a rat model of atrial remodeling induced by myocardial infarction (dilated atria) which reproduces the substrate of AF to investigate the mechanisms responsible for Kv1.5 channel internalization. Kv1.5 protein was decreased by 30% in dilated atria. However, the whole-cell current as measured by patch-clamp was maintained in dilated myocytes. The discrepancy between reduced protein level and maintained current density suggest that in dilated myocytes more Kv1.5 functional channels are inserted into the sarcolemma. We thus studied the internalization of Kv1.5 channels in control and diseased atria. Firstly, we investigated the endocytosis pathway for Kv1.5 channels in the atria. High resolution 3-Dimensionnal microscopy revealed that Kv1.5 channels are associated with clathrin vesicles in atrial myocytes but not with caveolin. Electron microscopy (EM) showed that vesicles are found both at the lateral sarcolemma and at the intercalated disc. Blockade of the clathrin pathway using hypertonic media or SiRNA nduced an increase in IKur, an accumulation of Kv1.5 channels at the sarcolemma as shown by biotinylation assays and an increased fluorescence recovery after photobleaching (FRAP), supporting the idea that Kv1.5 channels are internalzed via the clathrin pathway. Secondly, we studied the internalization activity in the dilated atria. In dilated atria, Western blot experiments showed a 35% reduction in clathrin levels. High resolution 3-Dimensionnal microscopy showed reduced association between Kv1.5 channels and clathrin vesicles in dilated myocytes. However, EM showed no significant difference in the internalization activity between sham and dilated atria. Therefore, the reduced clathrin protein synthesis observed in dilated atria is not likely to be responsible for the accumulation of Kv1.5 channels at the sarcolemma. Other mechanisms such as increased recycling and/or membrane stabilization must be investigated to understand how IKur is maintained n dilated atria and during chronic AF. [ABSTRACT FROM AUTHOR]

MAGUK proteins are a superfamily of proteins implicated in the anchoring and scaffolding of macromolecular complexes at the plasma membrane. The MAGUK protein CASK differs from other MAGUKs as it possesses an N-terminal calcium/calmodulin-dependant protein kinase domain, a single PDZ domain and has the capacity to translocate to the nucleus, where it acts as a co-activator to induce the transcription of T-element containing genes. However, apart from the fact that it is expressed in the heart, little else is known about its function in this organ. We found that CASK was expressed at the protein level in rat and human myocardia. Immunostainings of myocardial cryosections revealed that CASK was located at the lateral membrane of myocytes in sharp-contrast with the other cardiac MAGUKs, SAP97 and ZO1, which are found at the intercalated disc. CASK belongs to the costamere complex at the lateral membrane as it colocalized with syntrophin/dystrophin. Co-immunoprecipitation experiments performed on heart lysates showed that CASK and dystrophin interact. Moreover, in MDX mice which lack dystrophin, CASK was no longer present at the lateral membrane of myocytes, confirming that CASK participates in the syntrophin/dystrophin costameric complex. We have previously demonstrated that cardiomyocytes express two distinct pools of Nav1.5 channels: one at the intercalated discs interacting with SAP97 and a second at the lateral membrane interacting with the syntrophin/dystrophin complex. Due to its particular location, we hypothesized that CASK was involved in the targeting of the subpopulation of Nav1.5 channels to the lateral membrane. GST pull down experiments performed on heart lysates showed that CASK interacts with Nav1.5. In addition, immunostainings revealed that CASK and Nav1.5 colocalize in freshly isolated myocytes. Furthermore, in a HEK293 cell line stably expressing Nav1.5 channels, whole-cell patch clamp recordings showed that CASK silencing enhanced the sodium current (INa) (at -30mV, -95.1 ± 10.9 pA/pF, n=12 vs control -51.4 ± 5.7 pA/pF, n=13; mean ± SEM, p<0.01) while CASK overexpression decreased INa (at -30mV, -58.6 ± 10.2 pA/pF, n=8 vs control 88.6 ± 10.6 pA/pF, n=6; mean ± SEM, p<0.05). Finally, in cultured rat atrial myocytes where CASK was silenced, INa was also enhanced. In conclusion, CASK is a new cardiac MAGUK protein which shows unique cell localization. Our results indicate that CASK is present at the costamere level where it interacts with dystrophin. Interestingly, CASK is able to regulate the Nav1.5-mediated current suggesting that it is a new partner of the Nav1.5 macromolecular complex specifically at the lateral membrane. These results characterize a previously unreported ion channel partner and provide new insight into the regulation and organization of cardiac ion channels. [ABSTRACT FROM AUTHOR]

Cloud Computing becomes the next generation architecture of IT Enterprise. In contrast to traditional solutions, Cloud computing moves the application software and databases to the large data centers, where the management of the data and services may not be fully trustworthy. This unique feature, however, raises many new security challenges which have not been well understood. In cloud computing, both data and software are fully not contained on the user's computer; Data Security concerns arising because both user data and program are residing in Provider Premises. Clouds typically have a single security architecture but have many customers with different demands. Every cloud provider solves this problem by encrypting the data by using encryption algorithms. This paper investigates the basic problem of cloud computing data security. We present the data security model of cloud computing based on the study of the cloud architecture. We improve data security model for cloud computing. We implement software to enhance work in a data security model for cloud computing. Finally apply this software in the Amazon EC2 Micro instance. [ABSTRACT FROM PUBLISHER]

Cloud computing becomes the next generation architecture of IT Enterprise. Clouds are massively complex systems. They can be reduced to simple primitives, that are replicated thousands of times, and common functional units. The complexity of cloud computing create many issues related to security as well as all aspects of Cloud computing. One of the most important issues is data security. Clouds typically have a single security architecture but has many customers with different demands. The main focus of the proposed work is the data storage security in the cloud and the desktop. Generally, Data security is an important factor for both cloud computing and traditional desktop applications. This is to obtain the highest possible level of privacy. Modern Encryption algorithms play the main role in data security of cloud computing. We present an evaluation for selected eight modern encryption techniques namely: RC4, RC6, MARS, AES, DES, 3DES, Two-Fish, and Blowfish at two independent platforms namely; desktop computer and Amazon EC2 Micro Instance cloud computing environment. The evaluation has performed for those encryption algorithms according to randomness testing by using NIST statistical testing in the cloud computing environment. This evaluation uses Pseudo Random Number Generator (PRNG) to determine the most suitable technique and analysis the performance of selected modern encryption techniques. Cryptography algorithms are implemented using Java Cryptography Extensions (JCE). Simulation results are shown to demonstrate the effectiveness of each algorithm. [ABSTRACT FROM PUBLISHER]