EXPRESSION OF SODIUM-DEPENDENT PHOSPHATE (NA(D)PI) TRANSPORT IN XENOPUS-LAEVIS OOCYTES INDUCED BY MESSENGER-RNA FROM 1-ALPHA,25-DIHYDROXYVITAMIN D-3-TREATED RAT OSTEOBLAST-LIKE CELLS

Injection of messenger ribonucleic acid (mRNA) isolated from 1 alpha, 25-dihydroxyvitamin D-3-treated osteoblast-like (PyMS) cells leads to an enhanced sodium-dependent phosphate (NadPi) transport in Xenopus la evis oocytes, when compared to untreated cells. After mRNA size fracti onation, mRNA with an average size of 2.2-3.8 kilobases showed up to a 1.8-fold stimulation of Na(d)Pi transport encoding either directly a Na(d)Pi transporter(s) or proteins controlling their activity. No hybr idization was observed in Northern blots with RNA from rat bone or PyM S cells with the recently cloned rat renal brush border Na(d)Pi transp orter NaPi-2; hybrid depletion with a NaPi-2 antisense oligonucleotide did not abolish the PyMS mRNA-induced NadPi transport in oocytes. We present the first evidence for functional expression in Xenopus laevis oocytes of a new type of Na(d)Pi transport system in bone cells, whic h is different fi-om the renal type.