Expression of Na/Pi cotransport from opossum kidney cells in Xenopus laevis oocytes.

Xenopus laevis oocytes have been used for the expression of Na/Pi-cotransport activity by injections of poly(A)+ RNA (mRNA) isolated from an established renal cell line (OK cells). 3-5 days after mRNA injection, Na-dependent phosphate (Pi) uptake by oocytes was increased in a dose-dependent manner; there was no increase in Na-independent Pi uptake. Sucrose density-gradient fractionation indicated that the mRNA species encoding this activity is 2.4-2.8 kb in length. In Northern blots, using a cDNA probe related to human kidney-cortex Na/Pi-cotransport activity (NaPi-3), hybridization with a mRNA-species of 2.4-2.6 kb was obtained. Kinetic characterization ([Pi], [Na]) showed that expressed transport activity has properties similar to apical Na/Pi cotransport in OK cells.