Characterization of phosphate binding by alkaline phosphatase in rat kidney brush border membrane.

Phosphate binding by rat renal brush border membranes occurs on a single protein, as visualized by SDS polyacrylamide gel electrophoresis. The same protein can also be specifically labelled by gamma-32P ATP at 0 degree C or in the absence of magnesium. The phosphate binding protein co-migrates with monomers of two alkaline phosphatase activity bands previously localized on acrylamide gel.

Effects of L-bromotetramisole on phosphate transport by the proximal renal tubule: failure to demonstrate a direct involvement of alkaline phosphate.

Several recent studies have suggested that the alkaline phosphatase situated in the brush border membrane of the proximal convoluted tubule is positively related to inorganic phosphate reabsorption through this segment of the nephron. We examined this hypothesis by studying the influence of an inhibitor of alkaline phosphatase, L-bromotetramisole, upon phosphate transport through the isolated rabbit tubule, phosphate transport through brush border membrane vesicles of rats, and phosphate efflux from these vesicles. Results were compared with those obtained with D-bromotetramisole which is inactive on alkaline phosphatase.

Localization of immunoreactive vitamin D-dependent calcium binding protein in chick nephron.

Immunoreactive vitamin D-dependent calcium binding protein (iCaBP) has been localized in the chicken nephron, using microdissection and subsequent radioimmunoassay (RIA). Six to ten weeks old vitamin D-replete chicks were sacrificed and the kidneys removed. The various segments of the nephron, i.

Hormone-sensitive adenylate cyclase along the nephron of genetically hypophosphatemic mice.

The response of the adenylate cyclase (AC) activity to PTH and calcitonin was measured along the nephron of normal (N) and mutant hypophosphatemic (Hyp) mice of the C 57 BL/6J strain, using in vitro single tubule AC microassay. In each experiment, a Hyp mouse was paired to a N mouse from the same litter. In the presence of PTH (10 U/ml), AC activities (femtomoles cAMP per millimeter of tubule per 30-min incubation) were reduced in the proximal convoluted tubule of Hyp mice as compared to N mice in all experiments (448 +/- (SEM) 46 vs.

Magnesium handling by the papilla of the young rat.

In a recent study it was found that in Mg loaded rats, the fraction of filtered Mg (% E Mg) recovered in the bend of the loop of Henle of papilla was greater than the filtered load. However, the site of this Mg addition was unspecified and could be either the juxtamedullary proximal tubule, the pars recta, or in the papilla, the descending limb of the loop of Henle. In order to investigate the movement of Mg in the various structures of the papilla, we have studied: 1.

Micropuncture study of renal magnesium transport in magnesium-loaded rats.

Mg transport in the deep loop of Henle was studied in 15 young rats (50-60 g) after acute systemic Mg loading (UFMg (ultrafilterable Mg) 4.77 meq/liter). Intratubular Mg was measured with a recently described fluorometric microtechnique.