Sulfate transport by mouse renal cortical slices does not represent uptake by brush-border membrane.

We measured uptake of isotopically 35S-labelled sulfate anion by slices and by brush border membrane vesicles prepared from mouse renal cortex to identify: (i) whether metabolic incorporation of anion influences net transport; (ii) which membrane is primarily exposed in the renal cortex slice. Slices accumulated sulfate without significant incorporation into metabolic pools. Net uptake of sulfate at 0.1 mM by the slice occurred against an electrochemical gradient as determined by measurement of free intracellular sulfate concentration, the isotopic distribution ratio at steady-state, and the distribution of lipophilic ions (TPP+ and SCN-). Carrier mediation of sulfate transport in the slice was confirmed by observing concentration-dependent saturation of net uptake and counter-transport stimulation of efflux. Anion uptake was Na+-independent, K+- and H+-stimulated, and inhibited by disulfonated stilbenes. Brush-border membrane vesicles accumulated sulfate by a saturable mechanism dependent on a Na+ gradient (outside greater than inside); others have shown that uptake of sulfate by brush-border membrane vesicles is insensitive to inhibition by disulfonated stilbenes. These findings indicate that different mechanisms serve sulfate transport in renal cortex slice and brush-border membrane vesicle preparations. They also imply that the slice exposes an epithelial surface different from the brush-border, presumably the basolateral membrane, or its equivalent, since sulfate transport by slices resembles that observed with isolated basolateral membrane vesicles.

Double labelled T suppressor lymphocytes in the thymus of a patient with myasthenia gravis: morphological and immunological characteristics.

Double labelled lymphocytes were prevalent in the thymus of a 32-year-old woman with myasthenia gravis. The simultaneous presence of both E and C3b surface receptors was demonstrated. Focal paranuclear acid phosphatase activity of the cells supported their T cell origin. Histological analysis revealed a hyperplastic thymus with germinal centres in one lobe and an unusual transition to "thymoma-like" diffuse sheets of thymocytes and large thymic epithelial cells in the other lobe. Immunological studies of isolated cells from the "thymoma-like" region revealed a high percentage of E rosettes (96%), EAC rosettes (87%) and IgG-EA rosettes (60%). The large number of "active" rosettes (94%) indicated high avidity of receptors for sheep red blood cells. The postoperative accumulation of acid phosphatase positive T cells with C3b surface receptors in the peripheral blood was striking. These characteristics suggest that this cell population represents an activated T subset (TG) with a certain degree of immaturity similar to a particular stage of foetal T cell development (prothymocytes).