Age related changes in fluidity of rat renal brushborder membrane vesicles

Fluorescence anisotrophy of 1,6 diphenyl-1,3,5-hexatriene was determined in renal brushborder membranes prepared from rats 7, 14, 21 and 28 days of age, and adults, from 5 degrees C to 45 degrees C. There is a parallel relationship between temperature and mean fluorescence anisotrophy in the different age groups with a progressive decrease in fluidity with age. There is no phase transition apparent in membranes from any age group as evidenced by the lack of a fluorescence polarization "break point". There is also a linear relationship between limiting hindered anisotrophy and previously determined values for the height of the Na+-proline overshoot. This suggests that the physical characteristics of the renal brushborder membrane responsible for differences in fluidity are related to age-dependent transport alterations.