STIMULATIVE EFFECT OF Ba^<2+> ON p-AMINOHIPPURATE TRANSPORT IN RAT KIDNEY CORTICAL SLICES

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BaCl_2 stimulated significantly p-aminohippurate (PAH) accumulation in rat kidney cortical slices. The accumulation, however, was not stimulated by Sr^<2+>, Mn^<2+> and Mg^<2+>. Pretreatment of the slices with Ba^<2+> also increased PAH accumulation in the slices during incubation without BaCl_2. Kinetical analyses of PAH accumulation showed that the effect of Ba^<2+> was to increase V_<max>. No evidence for the effect of Ba^<2+> on PAH efflux from the slices was obtained. Thus, evidence indicating that Ba^<2+> stimulated PAH influx to the kidney cell was presented. Water distribution and energy metabolism in the slices were not related to the stimulative effect of Ba^<2+> on PAH accumulation. Ba^<2+> slightly lowered Na^<2+> concentration in the slices. However, in the presence of ouabain, further addition of Ba^<2+> recovered PAH accumulation to a control value in spite of poor Na^+ gradient as compared with that in control slices. Therefore, it is suggested that stimulation of PAH accumulation by Ba^<2+> was not due to changes in Na^+ gradient. No stimulation of tetraethylammonium (TEA), an organic base, transport system by Ba^<2+> was observed. These data suggest that Ba^<2+>specifically stimulates the organic acid transport system in rat kidney cortical slices by increasing PAH influx to the cells.
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