Developmental Aspects of Renal β-Amino Acid Transport. VI. The Role of Membrane Fluidity and Phospholipid Composition in the Renal Adaptive Response in Nursing Animals

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Abstract
Accumulation of the β-amino acid taurine is higher in adult rat renal brush border membrane vesicles than in nursing animals, which relates to a higher initial rate Vmax. A low sulfur amino acid diet increases and a 3% taurine diet reduces the Vmax of Na+ -taurine cotransport in brush border membrane vesicles at all ages after 7 days as compared to values on a normal diet. To determine if changes in membrane fluidity account for these developmental and adaptive events, the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene was used to measure fluorescence anisotropy. A two-component, single break curve fit the data over the range 4 to 56° C. Values for the break temperature centered around 23° C, not different than a break temperature determined in adult membranes. The values for membrane polarization range from 0.311 to 0.329 in membranes from 7-, 14-, and 21-day-old pups exposed to each of the three diets, significantly lower than the value in adult membranes (p < 0.02). The slopes of each component, equivalent to they apparent energy of activation, did not differ in relation to diet. The ontogenic changes in taurine uptake by brush border membrane vesicles related to the exposure to different dietary sulfur amino acid levels are not related to changes in membrane fluidity using 1,6-diphenyl-1,3,5-hexatriene as a probe. However, there is a decrease in fluidity with age. Total phospholipid content falls postweaning, and the percent of total content of phosphatidyl choline and glycerol phosphate fall, and phosphatidyl serine and ethanolamine rise as the rat ages. The results indicate that alterations in the phospholipid composition occur during the process of maturation and that changes in the fluidity of brush border membranes may account for maturational differences in Na+-dependent taurine transport.