Renal phosphate transport: Inhomogeneity of local proximal transport rates and sodium dependence
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- Baumann, K., de Rouffignac, C., Roinel, N. et al. Pflugers Arch. (1975) 356: 287. doi:10.1007/BF00580003
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The standing droplet method has been used in combination with the peritubular perfusion of blood capillaries to determine the build up of transtubular concentration differences of phosphate (Pi) in the renal proximal convoluted tubule of parathyroidectomized rats. Electron probe analysis was used to estimate Pi. At zero time both the intraluminal and the contraluminal Pi concentration was 2 mM. The time dependent decrease of the intraluminal Pi concentration was approximately 4 times faster in the early than in the late proximal convoluted tubule. After 45 sec an intraluminal steady state concentration of 0.20 mM Pi was achieved in the early part. In the late part the intraluminal Pi concentration approached a steady state value of 0.54 mM at 120 sec. When sodium free solutions were used the intraluminal Pi concentration increased to 2.22 mM in the earlier and to 2.76 mM in the late part. The data indicate that in the proximal convoluted tubule 1. The rate of phosphate reabsorption is greater in the early part than in the later part, and 2. phosphate reabsorption might occur as co-transport with Na+ ions.