Magnetic Effects in Cellular and Molecular Systems

Abstract

Chalazonitis and co-workers1 reported in 1970 that isolated frog rod outer segments in aqueous suspension can be oriented by a homogeneous magnetic field of 10 kG. The equilibrium orientation is parallel to the applied field. Furthermore, the two ends of a rod appear equivalent in a magnetic field. This latter observation suggested that the effect is either paramagnetic or diamagnetic. In either case, the effect can be due to (a) magnetic anisotropy, (b) “form” anisotropy, or (c) inhomogeneity of the applied field. The second and third mechanisms are ruled out, because the corresponding estimated magnetic potential (orientation) energy is not large enough to overcome thermal fluctuation. Numerical estimation based on the mechanism of magnetic anisotropy indicates that it is impossible to orient individual molecules in a rod with a field strength of 10 kG. However, two major molecular constituents, visual pigment rhodopsin and phospholipid, are oriented along the axial direction in a rod. If either molecule possesses a small anisotropy, the anisotropy will be additively summed in a rod and increased by a factor of 3 X 109 (rhodopsin) or 1013 (phospholipid). The crucial parameter is the summed anisotropy, which is the sum of the anisotropy of all the individual oriented anisotropic molecules, ∑ViΔXi, where ΔXi and Vi are the anisotropy of the volume susceptibility and the total effective volume of species i, respectively.