Non-Debye dielectric behavior and near-field interactions in biological tissues: When structure meets function

The Maxwell-Wagner theory of interfacial polarization treats dielectric particles suspended in homogeneous media and subjected to alternating fields as systems of independent induced dipoles, and therefore predicts simple Debye-type dispersion in which both permittivity and conductivity vary between low- and high-frequency plateaus. Unfortunately, Maxwell-Wagner theory cannot replicate its own success when applied to more concentrated and structured (i.e., non-random) systems of cells such as tissues. The effective medium theory, devised to incorporate contributions of the induced dipoles to the average far-field, brought about some improvement, but the general shape of the dielectric spectra remained that of a simple Debye - in contrast with experimental data. Supracellular organization of tissues induces non-Debye behavior due to near-field interactions between neighboring cells. Specifically, biological cells may perturb each other's electrical environment via dipolar (multipolar) fields or conductance bridges (such as pores and gap junctions) between cytoplasms and across cell membranes. We substantiate this hypothesis by presenting comparatively data from yeast and red blood cell suspensions, blood forming reversible supra-cellular structures, called 'rouleaux', breast tissues, as well as from brain treated with anesthetics that are known to affect the gap-junctional connectivity between cells. (C) 2010 Elsevier B.V. All rights reserved.