Streaming potential of human lumbar anulus fibrosus is anisotropic and affected by disc degeneration

The streaming potential responses of non-degenerate and degenerate human an ulus fibrosus were measured in a one-dimensional permeation configuration u nder static and dynamic loading conditions. The goal of this study was to i nvestigate the influence of the changes in tissue structure and composition on the electrokinetic behavior of intervertebral disc tissues. It was foun d that the static streaming potential of the anulus fibrosus depended on th e degenerative grade of the discs (p = 0.0001) and on the specimen orientat ion in which the fluid flows (p = 0.0001). For a statically applied pressur e of 0.07 MPa, the ratio of streaming potential to applied pressure ranged from 5.3 to 6.9 mV/MPa and was largest for Grade I tissue with axial orient ation and lowest for Grade III tissue with circumferential orientation. The dynamic streaming potential responses of anulus fibrosus were sensitive to the degeneration of the disc: the total harmonic distortion factor increas ed by 108%, from 3.92 +/- 0.66% (mean +/- SD) for Grade I specimens to 8.15 +/- 3.05% for Grades II and III specimens. The alteration of streaming pot ential reflects the changes in tissue composition and structure with degene ration. To our knowledge, this is the first reported data for the streaming potential of human intervertebral disc tissues. Knowledge of the streaming potential response of the intervertebral disc provides an understanding of potentially important signal transduction mechanisms in the disc and of th e etiology of intervertebral disc degeneration. (C) 1999 Elsevier Science L td. All rights reserved.