Levi M, Jameson D M, van der Meer B W
Department of Internal Medicine, Dallas Veterans Administration Medical Center, Texas.
Am J Physiol. 1989 Jan;256(1 Pt 2):F85-94. doi: 10.1152/ajprenal.1989.256.1.F85.
Renal tubular phosphate (Pi) transport is impaired in the aged rat. The decrement in Pi transport is manifested as a decrease in the Vmax of the luminal brush-border membrane (BBM) sodium-dependent Pi transport. In the present study we determined the potential role of alterations in cortical BBM lipid composition and fluidity in the age-related phosphaturia observed in rats. In the aged rat there are significant increases in the BBM cholesterol (Chol, 504 vs. 422 nmol/mg protein in adult, P less than 0.01) and sphingomyelin (Sph, 41.8 vs. 37.5 mol% in adult, P less than 0.01) and a decrease in the BBM fluidity [increase in fluorescence anisotropy of diphenylhexatriene (DPH), rDPH, 0.221 vs. 0.215 in adult, P less than 0.01]. The BBM lipid compositional and fluidity alterations may also play an important role in the impaired renal adaptation to a low-Pi diet in the aged rat. In the adult rat the renal adaptation to a low-Pi diet is associated with a decrease in BBM Chol (370 to 307 nmol/mg protein, P less than 0.01) and an increase in fluidity (decrease in rDPH 0.207 to 0.201, P less than 0.05). In the aged rat the renal adaptation to a low-Pi diet is incomplete and is associated with impaired ability to lower BBM Chol (441 to 429 nmol/mg protein, P = NS) and to increase fluidity (rDPH 0.211 to 0.211, P = NS). The results of this study therefore suggest that in the aged rat the increase in BBM Chol and Sph content, and the decrease in BBM fluidity play an important role in the impaired renal tubular Pi transport and adaptation to a low-Pi diet.
老年大鼠肾小管磷（Pi）转运受损。Pi转运的减少表现为管腔刷状缘膜（BBM）钠依赖性Pi转运的Vmax降低。在本研究中，我们确定了皮质BBM脂质组成和流动性改变在大鼠年龄相关性磷尿症中可能发挥的作用。老年大鼠的BBM胆固醇（Chol，成年大鼠为422 nmol/mg蛋白，老年大鼠为504 nmol/mg蛋白，P<0.01）和鞘磷脂（Sph，成年大鼠为37.5 mol%，老年大鼠为41.8 mol%，P<0.01）显著增加，BBM流动性降低[二苯基己三烯（DPH）荧光 anisotropy增加，rDPH，成年大鼠为0.215，老年大鼠为0.221，P<0.01]。BBM脂质组成和流动性改变在老年大鼠对低磷饮食的肾适应性受损中也可能起重要作用。成年大鼠对低磷饮食的肾适应性与BBM Chol降低（从370降至307 nmol/mg蛋白，P<0.01）和流动性增加（rDPH从0.207降至0.201，P<0.05）有关。老年大鼠对低磷饮食的肾适应性不完全，与降低BBM Chol（从441降至429 nmol/mg蛋白，P=无显著性差异）和增加流动性（rDPH为0.211至0.211，P=无显著性差异）的能力受损有关。因此，本研究结果表明，在老年大鼠中，BBM Chol和Sph含量增加以及BBM流动性降低在肾小管Pi转运受损和对低磷饮食的适应性中起重要作用。
