Stochastic Dynamics of Magnetosomes in Cytoskeleton

Rotations of microscopic magnetic particles, magnetosomes, embedded into the cytoskeleton and subjected to the influence of an ac magnetic field and thermal noise are considered. Magnetosome dynamics is shown to comply with the conditions of the stochastic resonance under not-too-tight constraints on the character of the particle’s fastening. The excursion of regular rotations attains the value of order of radian that facilitates explaining the biological effects of low-frequency weak magnetic fields and geomagnetic fluctuations. Such 1-rad rotations are effectively controlled by slow magnetic field variations of the order of 200 nT. PACS: 87.50.Mn; 87.10.+e; 87.16.Ac There are many hypothetical mechanisms suggested to explain the biological effects of weak low-frequency magnetic fields. A brief review of the mechanisms may be found in [1] and the detailed discussion in [2]. At the same time, the physical nature of these effects remains unclear. The basic problem is that the interaction energy of biologically active molecules and the MF at the geomagnetic level is very small [3]. It is much smaller than the energy of thermal fluctuations κT ≈ 4 · 10 erg at physiological temperatures. However, many organisms are well known to contain submicron magnetic particles. The energy of their turn in a weak magnetic field H is substantially greater than κT . For singledomain magnetite particles of radius r = 10 cm or 100 nm in the geomagnetic field the energy μH ≈ vJH equals approximately 24κT , where μ is the magnetic moment of the particle, v and J are the volume and the saturation magnetization. The cytoplasm near cell membranes features such visco-elastic properties that the turning of a microparticle may serve as a stimulus to cell division or ignite a nerve impulse. Magnetite particles found in the brain tissues of animals and humans are of particular interest: this constitutes one of the possible mechanisms of the weak MF effect on the human organism [4]. The nerve tissue of the brain is separated from the circulatory system by the blood-brain barrier which is impermeable for most chemicals. In turn, the circulatory system is separated from the digestive system. Therefore, relatively large ferroor ferrimagnetic particles cannot penetrate into brain tissue as a pollutant. They are found to have a biogenic origin, i.e. they appear over time as a direct result of the crystallization in brain matter. Biogenic magnetite particles are often called ‘magnetosomes’; they were first discovered in bacteria that displayed magnetotaxis [5]. The density of magnetosomes in the human brain is more than 5 · 10, and in meninges more than 10 crystals per gram [6]. In fact, about 90% of the particles measured in this study were 10–70nm in size, and 10% were 90–200nm. The particles were grouped into ensembles of 50–100 crystals.