EXPRESSION OF NA PI COTRANSPORT FROM OPOSSUM KIDNEY-CELLS IN XENOPUS-LAEVIS OOCYTES/

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