Theoretical impedance analysis of the intact rat lens with an ellipsoidal shells model]

We measured a.c. admittances for isolated rat lenses over a wide frequency range of 100 Hz to 500 MHz. In order to evade electrode polarization at low frequencies, we examined extracted lenses by direct semi-squeezing with Pt black-coated platinum electrodes. This gave rise to a 10(6) increment in permittivity at low frequencies, and two distinct dielectric dispersions were exhibited; dispersion 1 with a characteristic frequency (fc) of 2 kHz, and dispersion 2 with an fc of 2 MHz. In terms of loss tangent function, the two dispersions clearly dominated as two peaks. By curve fitting analysis with an allocated ellipsoidal-shells model based on ultrastructural features of the lens with a lens equivalent circuit, dispersion 1 was assigned to the equatorial cortex where regularly arranged lens fibers ran parallel to the applied electric field, and dispersion 2 to the nucleus of complicated fibers, combined with the polar cortex where lens fibers ran perpendicular to the electric field. Our results suggested that both lens dispersions were beta-dispersions attributable to bio-membranes.