A PUTATIVE GROWTH-RELATED RENAL NA-P-I COTRANSPORTER()

The mRNA that encodes for NaPi-2, the renal Na+-P-i cotransporter that is upregulated by P-i depletion in the adult rat, is low in the young animal. Yet, renal Na-P-i cotransport rates are higher in rapidly gro wing than in fully grown rats. The aim of this study was to unravel th e molecular basis of this apparent discrepancy. Poly(A) RNA obtained f rom the renal cortex of young animals induced higher rates of Na+-P-i cotransport in oocytes than equal amounts of poly(A) mRNA obtained fro m the renal cortex of mature rats. Moreover, poly(A) RNA obtained from renal cortex of rapidly growing animals treated with antisense NaPi-2 oligomers or depleted of NaPi-2 transcripts by subtractive hybridizat ion with cDNA generated from the renal cortex of adult rats retained i ts ability to induce Na+-P-i cotransport in oocytes. In addition, rena l poly(A) RNA of the young subjected to subtraction hybridization gene rated a 379-base pair reverse transcript ase-polymerase chain reaction product common to all known type II Na+-P-i cotransporters. These obs ervations permit us to surmise that the high rates of Na+-P-i cotransp ort prevailing during growth are due, at least in part, to the express ion of a specific mRNA that is only partially homologous to that of Na Pi-2.