The ability of water and solutes to move through the cartilage matrix is important to the normal function of cartilage and is presumed to be altered in degenerative diseases of cartilage such as osteoarthritis and rheumatoid arthritis. Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) techniques were used to measure a self diffusion coefficient (D) for small solutes in samples of explanted cartilage for diffusion times ranging from 13 ms to 2 s. With a diffusion time of 13 ms, the intratissue diffusivity of several small solutes (water, Na+, Li+, and CF3CO2-) was found consistently to be about 60% of the diffusivity of the same species in free solution. Equilibration of the samples at low pH (which titrates the charge groups so that the net matrix charge of -300 mM at pH 8 becomes approximately -50 mM at pH 2) did not affect the diffusivity of water or Na+. These data, and the similarity between the D in cartilage relative to free solution for water, anions, and cations, are consistent with the view that charge is not an important determinant of the intratissue diffusivity of small solutes in cartilage. With 35% compression, the diffusivity of water and Li+ dropped by 19 and 39%, respectively. In contrast, the diffusivity of water increased by 20% after treatment with trypsin (to remove the proteoglycans and noncollagenous proteins). These data and the lack of an effect of charge on diffusivity are consistent with D being dependent on the composition and density of the solid tissue matrix. A series of diffusion-weighted proton images demonstrated that D could be measured on a localized basis and that changes in D associated with an enzymatically depleted matrix could be clearly observed. Finally, evidence of restriction to diffusion within the tissue was found with studies in which D was measured as a function of diffusion time. The measured D for water in cartilage decreased with diffusion times ranging from 25 ms to 2 s, at which point the measured D was roughly 40% of the diffusivity in free solution. Although changes in matrix density by compression or digestion with trypsin led to a decrease or increase, respectively, in the measured D, the functional change in measured diffusivity with diffusion time remained essentially unchanged. In a different type of study, in which bulk transport could be observed over long periods of time, cartilage was submerged in 99% D2O and MRI studies were performed to demonstrate the bulk movement of water out of the cartilage matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantification of the dependence of cellular oxygen uptake rate (OUR) on oxygen partial pressure is useful for the design and testing of bioartificial devices which utilize cells. Thus far, this information has only been obtained from suspended cells and from cells attached to microcarriers. In this work, a device was developed to obtain the dependence of OUR on oxygen partial pressure for anchorage-dependent cells cultured in standard culture dishes. The device is placed and sealed on the top of the culture dish, and holds a Clark polarographic mini-electrode flush with the bottom surface of the device. It also houses a motor to spin a magnetic stir bar within the cell chamber to insure that the medium is well-mixed. Several characteristics of the device--such as oxygen leakage into the device chamber, electrode-lag time, and linearity of the electrode at low oxygen partial pressures--were quantified and their potential effect on the values of Vm (maximal OUR) and K0.5 (oxygen partial pressure at which OUR is half-maximal) were evaluated. Comparison of Vm and K0.5 values obtained with this device with previously published values for suspended rat hepatocytes, Bacillus cereus, and E. coli indicated that the technique provides values accurate within 30% as long as the cell under study has a K0.5 greater than approximately 1.0 mmHg. For hepatocytes cultured on 0.05 mm thickness collagen gel for 1 day (n = 4) and 3 days (n = 6), Vm was found to be 0.38 +/- 0.12 and 0.25 +/- 0.09 nmol O2/S/10(6) cells, respectively, and K0.5 was found to be 5.6 +/- 0.5 and 3.3 +/- 0.6 mmHg, respectively. This technique should aid in predicting bioreactor conditions such as flow rate, cell density, distance of cell from flow, and gas phase oxygen partial pressure which can lead to oxygen limitations. In addition, further studies of the effect of factors such as extracellular matrix composition, metabolic substrate, and drugs on the dependence of OUR on oxygen partial pressure for many anchorage-dependent cell types can be pursued with this technique.