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Biomedical subjects

R Kinne

Publications and source records attributed to R Kinne.

At least 91 records · Page 5Linked to original sources
PubMed1979

Effect of dietary phosphate intake on phosphate transport by isolated rat renal brush-border vesicles.

Renal brush-border membrane vesicles isolated from rats kept for 6-8 weeks on a low-phosphate diet (0.15% of dry matter) showed a markedly faster Na(+)-dependent phosphate uptake than did membrane vesicles isolated from animals kept on a high-phosphate diet (2% of dry matter). Phosphate-uptake rate by brush-border membrane vesicles isolated from animals on a low-phosphate diet remained significantly increased after acute parathyroidectomy. Dietary adaptation was also observed in animals that had been parathyroidectomized before exposure to the different diets. In animals on the low-phosphate diet parathyrin administration inhibited phosphate uptake by brush-border vesicles only if the animals were repleted with P(i) (5ml of 20mm-NaH(2)PO(4)) 1h before being killed. After acute phosphate loading and parathyrin administration the difference in the transport rate between the two dietary groups remained statistically significant. The results suggest that the adaptation of proximal-tubule phosphate transport to dietary intake of phosphate is reflected in the Na(+)/phosphate co-transport system located in the luminal membrane of the proximal-tubule cell. Since the dietary effects on phosphate transport by brush-border membranes are only partially reversed by acute changes in parathyrin concentration and are also observed in chronically parathyroidectomized animals, the adaptation of the Na(+)/phosphate co-transport system to dietary phosphate intake seems to involve an additional mechanism independent of parathyrin.

Alkaline Phosphatase↗
PubMed1979

Phosphate transport by rat renal brush border membrane vesicles: influence of dietary phosphate, thyroparathyroidectomy, and 1,25-dihydroxyvitamin D3.

In the present work we have investigated whether the changes in the renal handling of inorganic phosphate (Pi) induced by 1) dietary Pi, 2) removal of parathyroid glands and 3, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], are associated with alterations in the Na-dependent Pi uptake by brush border membrane vesicles (BBMV) isolated from renal cortex. Sham-operated (SHAM) or thyroparathyroidectomized (TPTX) rats treated or not with 26 pmol/day of 1,25(OH)2D3 i.p. were fed low (0.2%) or high (1.2%) P diet for 7 days. The results showed that in SHAM, TPTX and TPTX+1,25(OH)2D3 the Pi uptake by BBMV was greater after low than high Pi diet. It was greater in TPTX than in SHAM counterparts fed either diets. In TPTX fed low or high Pi diet 1,25(OH)2D3 decreased the Pi uptake to the level observed in SHAM. A striking parallelism was found between variations in Pi uptake by BBMV and in the tubular Pi reabsorption of the whole kidney. The Na-dependent glucose, the mannitol uptake by BBMV, and the alkaline phosphatase activity in cortical homogenates and BBMV were not affected by the various treatments. Thus, dietary Pi, chronic TPTX and 1,25(OH)2D3 appear to specifically affect the Na-dependent Pi transport system bound to the brush border membranes of renal cortical tubules. The alterations observed at this membrane level could account, at least in part, for the changes induced by these factors on the overall tubular reabsorption of Pi.

Animals↗
PubMed1979

Calcium ion transport across plasma membranes isolated from rat kidney cortex.

Basal-lateral-plasma-membrane vesicles and brush-border-membrane vesicles were isolated from rat kidney cortex by differential centrifugation followed by free-flow-electrophoresis. Ca2+ uptake into these vesicles was investigated by a rapid filtration method. Both membranes show a considerable binding of Ca2+ to the vesicle interior, making the analysis of passive fluxes in uptake experiments difficult. Only the basal-lateral-plasma-membrane vesicles exhibit an ATP-dependent pump activity which can be distinguished from the activity in mitochondrial and endoplasmic reticulum by virtue of the different distribution during free-flow electrophoresis and its lack of sensitivity to oligomycin. The basal-lateral plasma membranes contain in addition a Na+/Ca2+-exchange system which mediates a probably rheogenic counter-transport of Ca2+ and Na+ across the basal cell border. The latter system is probably involved in the secondary active Na+-dependent and ouabain-inhibitable Ca2+ reabsorption in the proximal tubule, the ATP-driven system is probably more important for the maintenance of a low concentration of intracellular Ca2+.

Adenosine Triphosphate↗
PubMed1979

Further evidence for the existence of an intrinsic bicarbonate-stimulated Mg2+-ATPase in brush border membranes isolated from rat kidney cortex.

The aim of this study was to provide further evidence for the existence of a nonmitochondrial becarbonate-stimulated Mg2+-ATPase in brush border membranes derived from rat kidney cortex. A plasma membrane fraction rich in brush border microvilli and a mitochondrial fraction were isolated by differential centrifugation. Both fractions contain a Mg2+-ATPase activity which can be stimulated by bicarbonate. The two Mg2+-ATPases are stimulated likewise by chloride, bicarbonate, and sulfite or inhibited by oligomycin and aurovertin, though to different degrees. In contrast to these similarities, only the Mg2+-ATPase activity of the mitochondrial fraction is inhibited by atractyloside, a substance which blocks an adenine nucleotide translocator in the inner mitochondrial membrane. On the other hand, filipin, an antibiotic that complexes with cholesterol in the membranes inhibits exclusively the Mg2+-ATPase of the cholesterol-rich brush border membranes. Furthermore it could be demonstrated by the use of bromotetramisole, an inhibitor of alkaline phosphatase activity, that the Mg2+-ATPase activity in the membrane fraction is not due to the presence of the highly active alkaline phosphatase in these membranes. These results support the assumption that an intrinsic bicarbonate-stimulated Mg2+-ATPase is present in rat kidney brush border membranes.

Adenosine Triphosphatases↗
PubMed1979

p-Aminohippuric acid transport into brush border vesicles isolated from flounder kidney.

p-Aminohippuric acid (PAH) transport was investigated in brush border vesicles isolated from renal proximal tubules of the winter flounder. Three characteristics of carrier-mediated transport were demonstrated: 1) unlabeled PAH inhibited the uptake of [3H]PAH; 2)[3H]PAH efflux from the vesicles was stimulated in the presence of unlabeled PAH in the extravesicular medium; and 3) PAH influx was inhibited by 2,4-dinitrophenol (DNP) and 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene (SITS). D-Glucose plus a sodium gradient stimulated PAH uptake, as did a K2SO4 gradient plus valinomycin, suggesting that PAH is transported as an anion. In contrast, PAH uptake into a membrane fraction containing mainly basal-lateral plasma membranes exhibited a larger inhibition by probenecid but a smaller inhibition by unlabeled PAH and SITS. Thus, carrier-mediated transfer of PAH driven by the electrochemical potential difference for PAH is demonstrated in the brush border membrane of the flounder kidney.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1978

Taurocholate--sodium co-transport by brush-border membrane vesicles isolated from rat ileum.

Uptake of taurocholate into brush-border membrane vesicles isolated from rat small intestine by a Ca(2+) -precipitation method was investigated by using a rapid-filtration technique. Uptake of taurocholate by ileal brush-border membranes consisted of three phenomena: binding to the outside of the vesicles, transfer across the vesicle membrane and binding to the intravesicular compartment. The transport of taurocholate across the brush-border membranes was stimulated in the presence of Na(+) compared with the presence of K(+); stimulation was about 11-fold in the presence of a NaCl gradient (Na(o)>Na(i)), where the subscripts refer to ;outside' and ;inside' respectively, and 4-fold under equilibrium conditions for Na(+) (Na(o)=Na(i)). In the presence of a Na(+) gradient a typical ;overshoot' phenomenon was observed. Membranes preloaded with unlabelled taurocholate showed an accelerated entry of labelled taurocholate (tracer exchange) in the presence of Na(+) compared with the presence of K(+). The stimulation by Na(+) was observed only in membrane preparations from the ileum. Addition of monactin, an ionophore for univalent cations, decreased the Na(+)-gradient-driven taurocholate uptake. The Na(+)-dependent taurocholate transport showed saturation kinetics and the phenomenon of counterflow and was inhibited by glycocholate. Other cations such as Li(+), Rb(+) and Cs(+) could not replace Na(+) in its stimulatory action. When the electrical potential difference across the vesicle membrane was altered by establishing different diffusion potentials (anion replacement; K(+) gradient+/-valinomycin) a more-negative potential inside stimulated Na(+)-dependent taurocholate transport. These data demonstrate the presence of a rheogenic (potential sensitive) Na(+)-taurocholate co-transport system in ileal brush-border membranes and support the hypothesis that the reabsorption of bile acids in the ileum is a secondary active uptake.

Animals↗
PubMed1978

Is hexokinase present in the basal lateral membranes of rat kidney proximal tubular epithelial cells?

The possible presence of hexokinase in basal lateral membranes from rat kidney proximal tubules was investigated. Basal lateral membranes were obtained from homogenates of rat kidney cortex by differential centrifugation and free flow electrophoresis. They were further purified by density gradient centrifugation. Hexokinase activity was measured as the phosphorylation of D-[U14C]glucose. Throughout the purification of the membranes, the specific activity of hexokinase decreased while that of (Na+ + K+)-ATPase increased. Hexokinase activity in all fractions could be quantitatively accounted for in terms of cytosolic and mitochondrial enzyme contributions. It is concluded that there is no hexokinase activity in basal lateral membranes from rat kidney.

Adenosine Triphosphatases↗
PubMed1978

Effect of parathyrin on the transport properties of isolated renal brush-border vesicles.

The transport properties of brush-border membrane vesicles isolated by a calcium-precipitation method from the renal cortex of normal and parathyrin (parathyroid hormone)-treated rats were studied by a rapid-filtration technique. Parathyrin elicited a dose-dependent decrease in the Na+-dependent phosphate uptake by the brush-border membrane vesicles, but the uptake of D-glucose, Na+ and mannitol was not affected. A maximum inhibition of 30% was observed after the application of 30 U.S.P. units intramuscularly 1 h before the animals were killed. Intravenous infusion of dibutyryl cyclic AMP (0.5-1.5 MG) also decreased the phosphate uptake by the brush-border vesicles. Both dibutyryl cyclic AMP and parathyrin were ineffective when added in vitro to brush-border membrane vesicles isolated from normal rats. These data suggest that parathyrin exerts its action on the phosphate reabsorption in the renal proximal tubule by affecting the Na+/phosphate co-transport system in the brush-border membrane. The effects of parathyrin on Na+ and glucose transport, however, seem to be due to alterations to the driving forces for transport and not to the brush-border transport systems.

Animals↗
PubMed1978

Studies on the orientation of brush-border membrane vesicles.

Orientation of rat renal and intestinal brush-border membrane vesicles was studied with two independent methods: electron-microscopic freeze-fracture technique and immunological methods. With the freeze-fracture technique a distinct asymmetric distribution of particles on the two membrane fracture faces was demonstrated; this was used as a criterion for orientation of the isolated membrane vesicles. For the immunological approach the accessibility or inaccessibility of aminopeptidase M localized on the outer surface of the cell membrane to antibodies was used. With both methods we showed that the brush-border membrane vesicles isolated from rat kidney cortex and from rat small intestine for transport studies are predominantly orientated right-side out.

Alanine↗
PubMed1978

Properties of brush border vesicles isolated from rat kidney cortex by calcium precipitation.

Brush border membrane vesicles were isolated from rat kidney cortex by differential centrifugation in the presence of 10 mM calcium. Their properties were compared to brush border vesicles isolated by free-flow electrophoresis. By the calcium precipitation method membrane vesicles were obtained in a shorter time with a similar enrichment of brush border marker enzymes (11- to 12-fold for alkaline phosphatase and maltase), with a similarly reduced activity of the marker enzyme for basal-lateral plasma membranes and an almost identical protein composition as revealed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The transport properties of the two membrane preparations for D-glucose, L-phenylalanine, and phosphate are essentially the same; there is some indication for a lower sodium permeability of the vesicles prepared by the calcium precipitation method. The latter vesicles were also shown to exhibit sodium gradient stimulated uptake of L-glutamate.

Animals↗
PubMed1977

Studies on the binding characteristics of antimycin A and albumin in relation to the inhibitor activity of the complex on rat proximal tubular sodium transport.

As reported previously [11] Antimycin A is effective in inhibiting sodium transport of the proximal tubule only when applied to the luminal side and in the presence of albumin. Therefore the interaction of Antimycin A with albumin was examined with the technique of equilibrium dialysis. It was found that Antimycin A was bound to albumin at five sites with a dissociation constant of 2.5 X 10(-6) M. This finding suggests that Antimycin A is taken up by the tubular cell as an Antimycin A/albumin complex via pinocytosis. In the pinocytotic vesicle this complex probably dissociates, and free Antimycin A is released into the cytoplasm where it can reach it's sites of action in the mitochondria and at the plasma membrane. This uptake mechanism might provide a general method to incorporate substances into the cell which do not penetrate the plasma membrane.

Antimycin A↗
PubMed1977

Incorporation of D-glucose-, L-alanine- and phosphate-transport systems from rat renal brush-border membranes into liposomes.

An extract of soluble proteins was prepared from a rat kidney brush-border membranes by Triton X-100 solubilization followed by centrifugation for 1 h at 100000g. Its protein composition was markedly different from that of the brush-border membranes. Proteoliposomes were formed by co-sonication of the Triton X-100-free extract with a naturally occurring mixture of phospholipids extracted from rat kidney. These proteoliposomes were shown to contain Na+-stimulated D-glucose-, L-alanine- and phosphate-transport systems.

Alanine↗