Phosphate uptake by proximal cells isolated from rabbit kidney: role of dexamethasone

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Abstract
A single cell suspension was prepared from rabbit kidney cortex by gentle mechanical dissociation. The isolated cells were functionally intact and metabolically active, as indicated by exclusion of eosin dye, respiratory measurement, and ATP content. The isolated cells were shown to possess long microvilli, and their proximal origin was confirmed by enzymatic and glucose production studies. The uptakes of 0.1 mM phosphate (Pi) and 0.05 mM D-glucose at 37 degrees C were strongly dependent on the extracellular Na+. Incubation of the cells with parathyroid hormone (10 U/ml) for 20 min reduced 20-s Pi uptake by 20%. The addition of dibutyryl cAMP decreased Pi uptake, with a maximal effect at 10(-6) M. Incubation of cells with gluconeogenic substrates, under conditions in which glucose production was increased, did not promote any change in Pi accumulation. When incubated for 60 min at 37 degrees C in the presence of dexamethasone (Dex), the Na+-dependent Pi uptake was decreased by 29% at 10(-9) M and by 36% at 10(-7) M without modification of the glucose uptake. Replacing Dex by aldosterone (10(-7) M) remained without effect on Pi uptake. It is concluded that: renal cells isolated by our preparative method are mainly of proximal origin; isolated cells are a good model for studying the regulation of Pi uptake in the proximal tubule; and glucocorticoids have an acute specific effect on Pi transport detectable in vitro and this effect does not seem to be related to modifications of renal gluconeogenesis.