Effect of dietary phosphate on transport properties of pig renal microvillus vesicles

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Abstract
Dietary phosphate manipulation results in stable adaptive changes in the transport functions of microvillus membrane vesicles isolated from pig renal cortex. When assayed under sodium gradient conditions, phosphate uptake is enhanced 200–400% in vesicles prepared from animals maintained on a low-phosphate diet (0.22%) compared to high-phosphate diet controls (0.82%). When transport is assayed in sodium preequilibrated vesicles, a 100% enhancement of phosphate uptake is demonstrable. Stimulation of phosphate uptake into low-phosphate diet vesicles after the imposition of a sodium chloride gradient is equivalent if uptake is measured at pH 6.0 or 8.0 and can be kinetically characterized as resulting from a Vmax alteration in the phosphate transport system. Microvillus membrane vesicle phosphate transport is maximally stimulated after only 2 days of dietary deprivation. Although a longer period (1 and 2 wk) of phosphate restriction does not further stimulate phosphate transport, it does result in an inhibition of other sodium gradient-dependent transport systems (glucose, alanine). phosphate transport; phosphate restriction; glucose transport; brush-border vesicles Submitted on October 22, 1979 Accepted on April 25, 1980

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