INCREASE OF NA/P-I-COTRANSPORT ENCODING MESSENGER-RNA IN RESPONSE TO LOW P-I DIET IN RAT-KIDNEY CORTEX

Renal proximal Na/P-i-cotransport is increased in response to low dietary P-i intake. Recently, a cDNA (NaPi-2) related to the rat renal brush membrane Na/P-i-cotransporter has been cloned. In the present study, we used rats fed for 6 days with either a low P-i diet (LPD) or a high P-i diet (HPD), respectively. In parallel to an increased renal brush-border membrane Na/P-i-cotransport in LPD rats, there was also an increased content of NaPi-2 mRNA in renal cortex. After injection into Xenopus laevis oocytes, mRNA isolated from LPD rats induced a greater increase in Na/P-i-cotransport compared to mRNA from HPD rats. Hybrid depletion experiments suggested that mRNA induced Na/P-i-cotransport is related to NaPi-2. We conclude that chronic P-i deprivation leads to an increased brush border membrane Na/P-i-cotransport via an increase in the level of (NaPi-2) mRNA.