Dielectric Measurement of Individual Microtubules Using the Electroorientation Method

Abstract

Little is known about the electrostatic/dynamic properties of microtubules, which are considered to underlie their electrostatic interactions with various proteins such as motor proteins, microtubule-associated proteins, and microtubules themselves (lateral association of microtubules). To measure the dielectric properties of microtubules, we developed an experiment system in which the electroorientation of microtubules was observed under a dark-field microscope. Upon application of an alternating electric field (0.5-1.9 x 10(5) V/m, 10 kHz-3 MHz), the microtubules were oriented parallel to the field line in a few seconds because of the dipole moment induced along their long axes. The process of this orientation was analyzed based on a dielectric ellipsoid model, and the conductivity and dielectric constant of each microtubule were calculated. The analyses revealed that the microtubules were highly conductive, which is consistent with the counterion polarization model-counterions bound to highly negatively charged microtubules can move along the long axis, and this mobility might be the origin of the high conductivity. Our experiment system provides a useful tool to quantitatively evaluate the polyelectrolyte nature of microtubules, thus paving the way for future studies aiming to understand the physicochemical mechanism underlying the electrostatic interactions of microtubules with various proteins.

3-dimensional electrode patterning within a microfluidic channel using metal ion implantation

“…This technique may be especially useful when wanting to probe particular entities within a biological cell, in particular, to orient microtubules. 31 We utilize the same parameters as have been shown in the electro-orientation techniques of E. coli K12 described in previous work to align the bacteria to the electric field. 17 10 V pp at 10 MHz is applied across two electrodes to obtain a preferred alignment.…”

A critical assessment of the information processing capabilities of neuronal microtubules using coherent excitations

“…However, recent advances in nanoscale technologies are improving experimental conditions, allowing for serious investigations to take place. Thus, despite the inherent difficulties, a number of experiments have investigated either the intrinsic [25][26][27][28] or ionic [26,29,30] conductivities of MTs.…”

“…As well, Minoura and Muto [30] made an attempt to measure the ionic conductivity of MTs using an electric field to orient MTs in solution and found a conductivity of 150 mS/m corresponding to a resistance of 27 G /μm along the MT length. The overall picture of an induced dipole moment arising due to the polarizability of the MT counterion system suggested by Minoura and Muto is consistent with another study of ionic conductivity along electrically stimulated MTs in which isolated taxol-stabilized MTs were shown to conduct an electric pulse applied through a micropipette [29].…”

Self-Reduction Rate of a Microtubule

“…Thus, τ is proportional to the dielectric constant ǫ when k is measured in unit of V 0 . Experimental measurements of ǫ are still not definitive but predict values like ǫ = 8.41 [13], 1 < ǫ < 100 [14], etc. Also, if the charge of the mobile object which determines the tubulin state, |α or |β , is modified from −e of a single electron to −ne, its effect is to be reflected by replacing ǫ → ǫ/n 2 in the formulae below.…”