Abstract
In an attempt to identify the renal Na+/P1 cotransporter, Xenopus laevis oocytes were used to express mRNA isolated from the renal cortex of rat kidney. Na+-dependent uptake of P1 in oocytes, injected with mRNA, resulted in an increase of 2–4-fold as compared to oocytes injected with water. Both the new expressed and endogenous Na+-dependent P1 uptake activity were inhibited with 2 mM phosphonoformic acid (PFA). Expression of P1 uptake into oocytes was dose-dependent with the amount of mRNA injected. When mRNA was fractionated on a sucrose gradient a mRNA fraction of 2.5 kilobases expressed the Na+/P1 cotransport activity in oocytes. This fraction resulted in a 6-fold stimulation of Na+-dependent P1 transport when compared to oocytes injected with water. The Km and Vmax for Na+-dependent P1 uptake were 0.18 mM and 118 pmol/oocyte per 30 min, respectively.
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