STIMULATIVE EFFECT OF Ba²⁺ ON p-AMINOHIPPURATE TRANSPORT IN RAT KIDNEY CORTICAL SLICES

Abstract

BaCl₂ stimulated significantly p-aminohippurate (PAH) accumulation in rat kidney cortical slices. The accumulation, however, was not stimulated by Sr²⁺, Mn²⁺ and Mg²⁺. Pretreatment of the slices with Ba²⁺ also increased PAH accumulation in the slices during incubation without BaCl₂. Kinetical analyses of PAH accumulation showed that the effect of Ba²⁺ was to increase V_max. No evidence for the effect of Ba²⁺ on PAH efflux from the slices was obtained. Thus, evidence indicating that Ba²⁺ 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 Ba²⁺ on PAH accumulation. Ba²⁺ slightly lowered Na²⁺ concentration in the slices. However, in the presence of ouabain, further addition of Ba²⁺ 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 Ba²⁺ was not due to changes in Na⁺ gradient. No stimulation of tetraethylammonium (TEA), an organic base, transport system by Ba²⁺ was observed. These data suggest that Ba²⁺specifically stimulates the organic acid transport system in rat kidney cortical slices by increasing PAH influx to the cells.