Ontogeny of renal sulfate transporters: postnatal mRNA and protein expression

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Abstract
Renal reabsorption of inorganic sulfate changes during growth and development. We have studied the expression of two proximal tubular sulfate transporters, NaSi-1 and sat-1, during postnatal maturation. Both NaSi-1 and sat-1 mRNA levels increase postnatally, peaking at day 14, with a maximal tenfold increase in NaSi-1 and sat-1 mRNA levels compared with day 1. A similar age-dependent increase was observed for sodium-dependent and sodium-independent sulfate uptakes by injection of rat kidney mRNA into Xenopus oocytes. Western blot analysis of renal membranes from rats aged day 1 to day 77 showed no significant changes for NaSi-1 protein, whereas sat-1 protein levels paralleled mRNA expression, increasing from day 1 to day 14, followed by a decrease in protein levels thereafter. For NaSi-1 protein expression, translational or posttranslational mechanisms may maintain equal numbers of sulfate proteins on proximal tubular membranes during maturation, whereas sat-1 protein levels are in close agreement with mRNA changes. This is the first study to look at the ontogeny of renal sulfate transporter (NaSi-1 and sat-1) expression during postnatal maturation.

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