Mechanism of renal phosphate retention during growth

• Published in: Kidney international Vol. 49; no. 4; pp. 1023 - 1026
• Main Authors: Silverstein, Douglas, Barac-Nieto, Mario, Spitzer, Adrian
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY Elsevier Inc 01.04.1996; Nature Publishing
• Subjects: Age Factors; Animals; Base Sequence; Biological and medical sciences; Carrier Proteins - genetics; Carrier Proteins - metabolism; Conserved Sequence; Female; Fundamental and applied biological sciences. Psychology; Humans; Kidney Cortex - growth & development; Kidney Cortex - metabolism; Molecular Sequence Data; Nucleic Acid Hybridization; Oocytes - metabolism; Phosphates - metabolism; Polymerase Chain Reaction; Rats; RNA, Messenger - metabolism; Sodium-Phosphate Cotransporter Proteins; Sodium-Phosphate Cotransporter Proteins, Type II; Symporters; Transcription, Genetic - physiology; Vertebrates: urinary system; Phosphates; Rat; Growth; Biological transport; Rodentia; Retention; Young animal; Kidney; Vertebrata; Mammalia; Inorganic anion; Tubular reabsorption; Adaptation
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1038/ki.1996.148

Mechanism of renal phosphate retention during growth. We have previously demonstrated that the retention of phosphate required for growth is due to a a high Vmax of the Na+-Pi cotransport system located in the brush border membrane of the proximal tubule. Because of this and other similarities between adaptation of the kidney to a high Pi demand (growth) and that to low Pi supply, we measured the levels of NaPi-2 mRNA and cDNA present in kidney cortex of 3- and > 12-week-old rats. Like in Pi depletion, Western blots revealed that a 80 to 85kDa protein recognized by a polyclonal antibody directed against the N-terminal region of the NaPi-2 protein was 2.3-fold more abundant in renal microvilli of the young than of adult animals. However, unlike in Pi depletion, Northern blot analysis failed to reveal a significant difference between mRNA levels at the two ages. Furthermore, suppression of NaPi-2 mRNA activity by annealing with antisense oligomers, or removal of the NaPi-2 transcripts by subtractive hybridization did not affect the rate of Na+-Pi cotransport induced in oocytes by polyA RNA of rapidly growing animals, while abolishing the ability of the renal cortical polyA RNA of adult rats to encode for Na+-Pi cotransport. RT-PCR of subtracted polyA RNA using primers specific for a region conserved in NaPi type II (Pi modulated) cotransporters yielded a product that was 98% homologous with that region, despite the absence of NaPi-2 cDNA. The results of these experiments demonstrate that the polyA RNA from kidneys of young animals contains unique mRNA transcripts able to encode for a NaPi protein homologous to, but distinct from NaPi-2.