ORIGINAL PAPER Modelling the Role of Intrinsic Electric Fields in Microtubules as an Additional Control Mechanism of Bi-directional Intracellular Transport M. V. Sataric Æ L. Budinski-Petkovic Æ I. Loncarevic Æ J. A. Tuszynski Published online: 2 October 2008 Ó Humana Press Inc. 2008 Abstract Active transport is essential for cellular func- tion, while impaired transport has been linked to diseases such as neuronal degeneration. Much long distance trans- port in cells uses opposite polarity molecular motors of the kinesin and dynein families to move cargos along micro- tubules. 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 dif- ferential 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 free- dom 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. Keywords Microtubule  Tubulin  GTP  Kinesin  Dynein  Kink  Ferroelectric Ferroelectric Properties of Microtubules The methods of biochemistry have been instrumental in advancing our knowledge of cell biology over the past several decades. However, they mostly focus on binary interactions between proteins and other biomolecules. Biochemistry also considers various complicated signal transduction pathways to evoke long-range effects or responses, but some difficulties still persist in explaining various long-range effects that undoubtedly take place in cells. We believe that electrostatic and electrodynamic effects may play a much greater role in cell processes than hitherto assumed. It is known that associated proteins such as dynactin, klar, and rabs play a role in switching kinesin and dynein molecules on or off. However, this does not exclude the possibility that these interactions could be initiated, affected, or time- and space-ordered by moving ionic waves or dipole moment changes brought about by propagating kinks with a finely tuned amplitude and speed. A propagating kink wave moving in one direction could cause a kinesin molecule to switch on or off depending on the particular situation. In this connection, dipole moments and ferroelectric properties of biomolecules may be of crucial importance. Large polar molecules, ferroelectric (FE) polymers, and ferroelectric/ferroelectric liquid crystals, represent M. V. Sataric  L. Budinski-Petkovic  I. Loncarevic Faculty of Engineering, University of Novi Sad, Trg D. Obradovica 6, 21000 Novi Sad, Serbia J. A. Tuszynski (&) Experimental Oncology, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada e-mail: jtus@phys.ualberta.ca Cell Biochem Biophys (2008) 52:113–124 DOI 10.1007/s12013-008-9028-1