ACCUMULATION OF SULFATE LABELLED WITH S³⁵ BY RAT TISSUE IN VITRO

Rat kidney slices incubated in vitro may show, in parallel with other shifts in electrolyte content, a striking capacity for accumulating sulfate ion (sulfate labelled with S³⁵). The uptake is reversed or reduced by CN^-, cooling to room temperature, and by interference with adequate oxygenation. Under the conditions of the experiment, the presence in the medium of sodium acetate and glucose as substrates was found to be without measurable effect on the accumulation. The extent of sulfate uptake is related to the ionic composition of the medium in which the tissue is incubated, for the uptake occurs optimally only in the presence of a K⁺ level of about 0.04 M, and is decreased as the concentration of Na⁺ rises. Likewise, when Ca⁺⁺, Mg⁺⁺, or choline is present in the medium, sulfate accumulation may be depressed. In addition to renal cortex, kidney medulla and liver showed capacity for sulfate accumulation, whereas no convincing evidence for significant uptake was obtained with strips of aorta, colon, or diaphragm.