Modelling the role of intrinsic electric fields in microtubules as an additional control mechanism of bi-directional intracellular transport.

Active transport is essential for cellular function, while impaired transport has been linked to diseases such as neuronal degeneration. Much long distance transport in cells uses opposite polarity molecular motors of the kinesin and dynein families to move cargos along microtubules. It is clear that many types of cargo are moved by both sets of motors, and frequently in a reverse direction. The general question of how the direction of transport is regulated is still open. The mechanism of the cell's differential control of diverse cargos within the same cytoplasmic background is still unclear as is the answer to the question how endosomes and mitochondria move to different locations within the same cell. To answer these questions we postulate the existence of a local signaling mechanism used by the cell to specifically control different cargos. In particular, we propose an additional physical mechanism that works through the use of constant and alternating intrinsic (endogenous) electric fields as a means of controlling the speed and direction of microtubule-based transport. A specific model is proposed and analyzed in this paper. The model involves the rotational degrees of freedom of the C-termini of tubulin, their interactions and the coupling between elastic and dielectric degrees of freedom. Viscosity of the solution is also included and the resultant equation of motion is found as a nonlinear elliptic equation with dissipation. A particular analytical solution of this equation is obtained in the form of a kink whose properties are analyzed. It is concluded that this solution can be modulated by the presence of electric fields and hence may correspond to the observed behavior of motor protein transport along microtubules.

Memory effects in vibrated granular systems: response properties in the generalized random sequential adsorption model.

We investigate, by numerical simulation, the dynamical response of a granular system to an abrupt change in shaking intensity within the framework of the reversible random sequential adsorption models. We analyse the two-dimensional lattice model in which, in addition to the adsorption-desorption process, there is diffusion of the adsorbed particles on the surface. Our model reproduces qualitatively the densification kinetics and the memory effects of vibrated granular materials. An interpretation of the simulation results is provided by the analysis of the insertion probability function. The importance of the diffusional relaxation is discussed. We conclude that a complex time-evolution of the density could be explained as a consequence of the variation of the diffusion rate during the compaction. We study the nonequilibrium time-dependent density-density autocorrelation function and show that the model displays out-of-equilibrium dynamical effects such as aging.

[Dynamic thermoplastic cervico-thoracic orthoses in conservative and postoperative treatment of congenital torticollis]. / Dinamicna termoplasticna cervikotorakalna ortoza za konzervativno i postoperativno lecenje urodenog krivog vrata.

Contention of the corrected position of the rotation and anteflexion of the head and neck is very important for the congenital torticollis. Frequent reversion of the deformity was the consequence of the unproper passive and static cast bandages or rigid plastic and more functional leather-metal orthosis. Original dynamic cervico-thoracic orthosis, made of thermoplastic material, provides progressive, individual and stable correction and contetion of the best possible head and neck position. The value of the applied orthosis is proved by the excellent results in treatment of 12 non-operated children and 16 postoperative treated children that suffered of primary myogenic torticollis.

[Ultrasonic diagnosis of transitory synovitis of the hip joint in children]. / Ultrazvucna dijagnostika tranzitornog sinovita decijeg kuka.

The most common cause of a limp in childhood is transitory synovitis of the hip. At the Paediatric Surgery Clinic in Novi Sad, in the period from 1989 to 1991, 58 children were treated for hip transitory synovitis and the diagnosis was confirmed by ultrasonic finding of the exudate in the joint. The ultrasonic investigation of the hips was performed by using Siemens and Kretz scanners equipped with 5 MHz linear or sector transducers. The approach to the hip was frontal and the lower extremity has been in the neutral position. The distance between the femoral neck and the joint capsule was verified according to the Adam's morphometric procedure. The measured pathological values were from 7 mm to 14 mm (normal values are from 2 mm to 4 mm). In the routine transitory synovitis diagnosis, real-time arthrosonography of the hip shows high sensitivity, accuracy and selective values compared to other diagnostic procedures.