Renal adaptation to dietary phosphate deprivation: role of proximal tubule brush-border membrane fluidity
Levine, B.S.; Knibloe, K.A.; Golchini, K.; Hashimoto, S.; Kurtz, I.
American Journal of Physiology 260(5 Pt 2): F613-F618
1991
ISSN/ISBN: 0002-9513 PMID: 2035648 Document Number: 387063
With dietary phosphate (Pi) restriction, fluidity of renal proximal tubule brush-border membranes (BBM) and Na-dependent Pi transport (Na-Pi) are increased, suggesting that changes in BBM fluidity are critical for adaptation to Pi restriction. To test this hypothesis, the temporal relationship between Na-Pi transport and changes in BBM fluidity was assessed after Pi deprivation in rats. Renal cortex was obtained from rats fed either a 0.03% (-P) or a 0.6% (+P) Pi diet for 4 h or 7 days, and BBM were prepared. Na-Pi uptake by BBM was measured by use of rapid filtration, and BBM fluidity was assessed by use of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). After 4 h on the diets, Na-Pi uptake was 439 +/- 142 (SD) and 984 +/- 184 pmol.mg protein-1.5 s-1 in +P and -P, respectively (P < 0.01, n, = 8). Na-dependent proline uptake was unchanged. DPH anisotropy and total cholesterol were similar between groups: 0.204 +/- 0.025 and 0.401 +/- 0.047 nmol/mg protein, respectively, in +P and 0.205 +/- 0.015 and 0.392 +/- 0.037 in -P (P > 0.05, n = 8-10). After 7 days, Na-Pi uptake was 841 +/- 291 in +P and 2,168 +/- 848 pmol.mg protein-1. 5 s-1 in -P, P < 0.01, n = 8. DPH anisotropy and BBM cholesterol were 0.175 +/- 0.019 and 443 +/- 132 nmol/mg protein, respectively, in +P and 0.162 +/- 0.020 (n = 8) and 341 +/- 128 (n = 3) in -P (P < 0.05). Na-Pi transport was also assessed after in vitro manipulation of BBM fluidity. Exposure of BBM to either 200 mM butanol, 12 mM hexanol, or 3.5 mM heptanol lowered DPH anisotropy as follows (in nmol/mg protein): vehicle, 0.166 +/- 0.005; butanol, 0.142 +/- 0.006; hexanol, 0.146 +/- 0.006; and heptanol, 0.136 +/- 0.009 (P < 0.05, n = 5). Na-Pi uptake was as follows (in pmol.mg protein-1.5 s-1): vehicle, 345 +/- 55; butanol, 257 +/- 41 (P < 0.05, n = 5); hexanol, 398 +/- 28; and heptanol, 356 +/- 57. Each anesthetic agent lowered Na-proline transport. Lower doses of anesthetic agents had little effect on Na-Pi uptake despite decreasing DPH anisotropy. In summary, increases in BBM Na-Pi transport occurred before changes in BBM fluidity or BBM cholesterol; changes in BBM fluidity are not critical for early adaptation. Furthermore, changes in BBM Na-Pi transport did not correlate with changes in BBM fluidity induced in vitro.