Factors influencing the growth and respiration of rat cerebral astrocytes in primary culture

Cell densities and respiratory rates of astrocytes from neonatal rat brain grown in primary culture were determined after 20–30 days in vitro. Cells grown in flasks reached lower densities (g DNA/cm²) and higher protein: DNA ratios than cells grown in petri dishes. Respiratory rates were lower for cells grown in flasks compared to cells grown in dishes. The pH of the medium in flasks fell below 6.9 between feedings while the pH of the medium in dishes remained at about 7.2. Cells grown in dishes with the medium pH adjusted to 6.8 also showed lower final cell densities, higher protein: DNA ratios, and lower respiratory rates, compared to cells grown under similar conditions at pH 7.5. Intermediate values of each parameter were found in cells grown at pH 7.5 for one week and then at 6.8 for 20 days. We conclude that the effects of ambient pH account for the differences in growth characteristics and respiratory rates of astrocytes grown in dishes versus those grown in flasks.     

Sedimentation velocity of sodium hyaluronate-lysozyme mixtures

A study of the sedimentation behaviour of lysozyme in sodium hyaluronate (Na-HA) solution and of the Na-HA medium itself, has been carried out to determine whether the strongly basic enzyme lysozyme forms complexes with Na-HA at physiological ionic strength. At typical physiological salt concentration, 0.146 m NaCl, and also in 0.100 M NaCl, lysozyme sedimentation in an Na-HA solution can be adequately described as independent sedimentation of a slightly associated protein through a three-dimensional network acting partially as a macromolecular sieve. The s_20,w of lysozyme when determined in 0.146 M NaCl, indicated partial aggregation of the enzyme at this salt concentration. Decreases in sedimentation coefficients of lysozyme with increase in Na-HA concentration show a pronounced sieving effect by the equality of observed sedimentation coefficient of lysozyme and Na-HA at higher Na-HA concentrations, but typically individual sedimentation coefficients when the macromolecular mixture was diluted approximately ten-fold.