1) Department of Mathematics and Statistics, University of Edinburgh, Edinburgh EH9 3JZ, Great Britain 2) Research Laboratory of the Regional Narcological Center, St.Petersburg, Russia 3) I.M. Sechenov Institute of Evolutionary Physiology & Biochemistry St.Petersburg, RussiaV.A.Kaimanovich (1), E.M.Krupitski (2) and A.V.Spirov (3)
Microtubules (MT) play a key role in the vectorization of intracellular
movements. We consider theoretical mechanisms of the infuence of intracellular
electric fields on directed polymerization and orientation of MT. A generalization
of Fromherz' model of self-organization in the ionic channels system of
biomembranes is used for a simulation of the interaction between the membrane
electric activity and the behaviour of submembrane cytoskeletal components.
Numerical experiments show two possible scenarios of the system evolution
similar to (1) cortical waves of polymerization of the oocyte cytoskeleton
after fertilization and (2) the process of ooplasmic segregation in the
zygote of ascidia Clione. A similar interaction between the membrane
electric activity and directed polymerization of microtubules can also
play a fundamental role in neuronal mechanisms of learning and memory.
This document is the html version of the paper that appeared in the JOURNAL OF ELECTRO & MAGNETOBIOLOGY. 1994, 13, (2), 149-158.
Practically all intracellular components perform directed (vectorized) movements (1-3). All kinds of macromolecules directionally move in the hyaloplasm to different regions of the cell, inside membrane organoids (e.g., inside EPR) and laterally in membranes (4-8). These movements compartmentalize metabolic processes in the cell.
Many cell organoids also perform directed movements: mitochondrions (to areas of intensive metabolism) (9), chloroplasts (to light), lysosomes (to phagocytic vacuoles), nuclei (1), secretory and endocytic vesicles (membrane recycling) (1, 2), Golgi apparatus (10), centrioles, etc.
A key role in the vectorization of all above listed intracellular movements belongs to the microtubules (MT) (3, 6, 8, 9, 11-14). Destruction of MT makes directed movements of the intracellular components impossible and, as a consequence, it leads to disturbances in the cell form and structure (3, 11). However, concrete mechanisms of directed polymerization and orientation of MT are still not quite clear.
On the other hand, vectorization of in tracellular processes is determined by electrical fields and ion gradients, the latter having been observed practically in all cells (15, 16). Disturbances of these electrical gradients force pronounced disturbances of directed intracellular movements (17). Electrical fields with intensity close to experimentally observed in cells (up to 400 V/m according to (18)) lead to cell polarization and determine directions of cell motility (19, 20).
Thus, one can ask about a direct relationship between directed MT polymerization and intracellular electric fields.
Experiments of Vassilev et al. (21) show that electric fields of intensity comparable with that of intracellular fields affect polymerization of the tubulin solution in vitro in such a way that the resulting MT are oriented along the field. A theoretical mechanism explaining how electric fields may induce directed polymerization of MT in vivo was proposed in (22, 23).
It is well known that electric polarity of cells is caused by asymmetry and/or heterogeneity of the distribution of the ion pumps and channels in cell membranes. This asymmetry leads to a charge redistribution in the cell, i.e., to creation of non-zero electrical gradients in the cell (15, 16). These processes can be described by Fromherz' "cell self-electrophoresis" model (24).
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