Static compression of articular cartilage can reduce solute diffusivity and partitioning: implications for the chondrocyte biological response

Chondrocytes depend upon solute transport within the avascular extracellula r matrix of adult articular cartilage for many of their biological activiti es. Alterations to bioactive solute transport may, therefore, represent a m echanism by which cartilage compression is transduced into cellular metabol ic responses. We investigated the effects of cartilage static compression o n diffusivity and partitioning of a range of model solutes including dextra ns of molecular weights 3 and 40 kDa, and tetramethylrhodamine (a 430 Da fl uorophore). New fluorescence methods were developed for real-time visualiza tion and measurement of transport within compressed cartilage explants. Exp erimental design allowed for multiple measurements on individual explants a t different compression levels in order to minimize confounding influences of compositional variations. Results demonstrate that physiological levels of static compression may significantly decrease solute diffusivity and par titioning in cartilage. Effects of compression were most dramatic for the r elatively high molecular weight solutes. For 40 kDa dextran, diffusivity de creased significantly (p<0.01) between 8% and 23% compression, while partit ioning of 3 and 40 kDa dextran decreased significantly (p<0.01) between fre e-swelling conditions and 8% compression. Since diffusivity and partitionin g can influence pericellular concentrations of bioactive solutes, these obs ervations support a role for perturbations to solute transport in mediating the cartilage biological response to compression. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.