Transport of tricarballylate by intestinal brush-border membrane vesicles from steers

Tricarballylic acid is a non-metabolizable rumen bacterial fermentation product of the naturally occurring tricarboxylic acid trans-aconitic acid. The aim of the present study was to investigate intestinal absorption of tricarballylate using brush-border membrane vesicles (BBMVs) isolated from the proximal jejunum of steers by a Ca2+ precipitation method with subsequent differential centrifugation. Transport of tricarballylate was investigated indirectly (influence of tricarballylate on the uptake of 14C-labelled citrate) as well as directly (uptake of 3H-labelled tricarballylate). Citrate as well as tricarballylate uptake (at a concentration of 0.05 mmol l-1) was strongly stimulated by an inwardly directed initial Na+ gradient. Furthermore, transport of both tricarboxylates under Na+ gradient conditions was clearly enhanced by lowering the extravesicular pH from 7.8 to 5.6. The imposition of an inwardly directed H+ gradient (pH(out)/pH(in) = 5.6/7.8) further enhanced the intravesicular accumulation of citrate as well as of tricarballylate compared with pH(out)/pH(in) = 5.6/5.6. Unequivocal evidence for a common transport site for tricarballylate and citrate was obtained from 'cis-inhibition' and 'trans-stimulation' of Na(+)-dependent citrate uptake by tricarballylate. In further experiments the influence of different substances on the uptake of 3H-labelled tricarballylate was evaluated. Unlabelled tricarballylate, citrate, succinate as well as trans- and cis-aconitate significantly inhibited the accumulation of 3H-labelled tricarballylate by BBMVs. Tricarballylate uptake as a function of the tricarballylate concentration revealed a Na(+)-dependent saturable component (apparent kinetic parameters: maximal transport capacity (Vmax) = 119 pmol (mg protein)-1 (3s)-1; affinity constant (Km) = 0.097 mmol l-1) and a Na(+)-independent diffusional component (diffusion constant: 169 nl (mg protein)-1 (3s)-1). It is concluded that tricarballylate and citrate are transported across the intestinal brush-border membrane by a common, Na(+)-dependent transport mechanism. The stimulatory influence of a low extravesicular pH most probably indicates that the protonated forms of tricarboxylates are better transported than the trivalent species.     

Uptake of doxifluridine by rabbit small intestinal brush-border membrane vesicles

Characteristics of the transport of doxifluridine (5'-DFUR) in rabbit small intestinal brush-border membrane vesicles were examined. 5'-DFUR was rapidly incorporated and a linear relation was found between the concentration of 5'-DFUR and its uptake rate in the concentration range tested (0.1-10 mM). The uptake rate increased at an acidic pH, at which 5'-DFUR is present mostly in an undissociated form. However, the uptake rate was not changed either by the extravesicular Na+ concentration or by the inside negative membrane potential. Nucleosides, uridine and adenosine only slightly inhibited the uptake, even at a fifty-fold concentration, and nucleobases, uracil and thymine had no effect. These results suggest the possibility of the major involvement of passive diffusion of the undissocated form of 5'-DFUR in the uptake of the drug through the brush-border membrane at a relatively high concentration.     

Characteristics of cefdinir uptake by rabbit small intestinal brush-border membrane vesicles

PURPOSE: To search for changes in the presence and distribution of the cell-adhesion-related HNK-1 carbohydrate epitope after cataract extraction. METHODS: Twenty-five pseudophakic and two aphakic human autopsy eyes and, for comparison, one anterior subcapsular cataract obtained at surgery were studied with monoclonal antibodies (MAbs) HNK-1 and NC-1 to the HNK-1 epitope using the avidin-biotinylated peroxidase complex method. RESULTS: MAbs to the HNK-1 epitope constantly immunolabelled the inner connective tissue layer of the ciliary body in all pseudophakic and aphakic eyes studied. The distribution of the immunoreaction was similar to that reported for normal eyes. They also labelled the extracellular matrix in each of 18 plaques of secondary cataract on the posterior capsule, in each of 13 plaques at the rim of the capsular bag, and in the anterior subcapsular cataract. Bladder cells in each of 16 Soemmering's rings remained unlabelled. CONCLUSION: The distribution of the HNK-1 epitope in the ciliary body does not appreciably change after cataract extraction, although the accommodative demand of the eye is altered. Its presence in an anterior subcapsular cataract suggests that the epitope may be locally produced by lens epithelial cells also in secondary cataract. The epitope is associated with cell adhesion and migration, both of which may play a role in the pathogenesis of secondary cataract.     

Modulation of putrescine transport in rat intestinal brush-border membrane vesicles by fasting and refeeding

Fasting and refeeding dramatically alter small intestinal mucosal growth which is greatly dependent on polyamine biosynthesis and transport. The aim of this study was therefore to examine the uptake of the diamine putrescine by brush-border membrane vesicles from the small intestine of rats fasted for 3 days or refed a standard diet after a PERIOD OF FASTING. WHILE THE MICHAELIS-MENTEN CONSTANT KM WAS essentially unaltered, the maximum velocity (Vmax) for putrescine uptake was 1.85-fold higher in fasted animals than in ad libitum-fed controls. Refeeding fasted rats for 24 h caused a 31% decrease in the Vmax value that, however, remained 1.27-fold higher than in control RATS, WHILE THE KM VALUE WAS STILL UNCHANGED. FASTING RATS OR refeeding rats after a period of fasting caused only a 13 or 17% increase, respectively, in the value of the constant for the nonsaturable component (P) of putrescine transport relative to the corresponding control condition. Our study also confirms that both the mucosal polyamine biosynthesis and intestinal content are altered by fasting. We suggest that an increased uptake activity may have a conservative role by preventing a substantial loss of tissue polyamines during fasting.     

pH-dependent fluoride transport in intestinal brush border membrane vesicles

Ciliary neurotrophic factor (CNTF) exerts a multiplicity of effects on a broad spectrum of target cells, including retinal neurons. To investigate how this functional complexity relates to the regulation of CNTF receptor alpha (CNTFR alpha) expression, we have studied the developmental expression of the receptor protein in chick retina by using immunocytochemistry. During the course of development, the receptor is expressed in all retinal layers, but three levels of specificity can be observed. First, the expression is regulated temporally with immunoreactivity observed in ganglion cells (embryonic day 8 [E8] to adult), photoreceptor precursors (E8-E12), amacrine cells (E10 to adult), bipolar cells (E12-E18), differentiated rods (E18 to adult), and horizontal cells (adult). Second, expression is restricted to distinct subpopulations of principal retinal neurons: preferentially, large ganglion cells; subpopulations of amacrine cells, including a particular type of cholinergic neuron; a distinctly located type of bipolar cell; and rod photoreceptors. Third, expression exhibits subcellular restriction: it is confined largely to dendrites in mature amacrine cells and is restricted entirely to outer segments in mature rods. These data correlate with CNTF effects on the survival of ganglion cells and mature photoreceptors, the in vitro differentiation of photoreceptor precursors and cholinergic amacrine cells, and the number of bipolar cells in culture described here or in previous studies. Thus, our results demonstrate an exceptional degree of complexity with respect to the regulation of neuronal CNTFR alpha expression in a defined model system. This suggests that the same signaling pathway is used to mediate a variety of regulatory influences, depending on the developmental stage and cell type.     

Proline, leucine, and alanine transport in placental microvillous membrane vesicles prepared from late gestational rats

The aerodynamic particle-size distribution for two doses of a Becloforte metered-dose inhaler (MDI) was measured by use of a twin-stage impinger (TSI), the new multi-stage (five-stage) liquid impinger (MSLI) and the Andersen cascade impactor (ACI) (n = 5 for each apparatus). The mean (s.d.) fine-particle doses measured by the three techniques for the Becloforte MDI were 40.3 (1.2), 45.7 (0.5) and 41.8 (0.4)% w/w, respectively; the median mass aerodynamic diameters (MMAD) measured using the MSLI and the ACI were 3.50 and 3.73 microns, respectively. The MSLI fine particle (< 6.8 microns) doses for 2, 5, 10, 20, 30 and 40 doses from Becloforte MDIs (n = 5 for each dose) were 49.7 (0.7), 52.9 (1.2), 45.3 (0.6), 45.5 (0.71), 45.9 (0.7) and 46.4 (0.7)% w/w, respectively. Values obtained using the ACI (< 5.8 microns) were 40.8 (1.0), 41.0 (0.8), 44.4 (0.5), 43.1 (0.4), 42.8 (0.5) and 40.4 (0.4)% w/w (n = 4). MMAD values measured with the MSLI were 3.39, 3.46, 3.75, 3.91, 4.15 and 4.45 microns, respectively; using the ACI they were 3.46, 3.54, 3.61, 3.66, 3.73 and 3.85 microns. The results indicate that the measured aerodynamic particle-size distributions of beclomethasone dipropionate MDIs are affected by the dose dispensed and by the apparatus used for measurement.     

Effects of fatty acid sucrose esters on ceftibuten transport by rat intestinal brush-border membrane vesicles

The effects of fatty acid sucrose esters on membrane lipid dynamics and ceftibuten transport by rat intestinal brush-border membrane vesicles (BBMV) were examined to clarify the differences in the action of mono- and poly-acyl sucrose esters on the drug transport. Fatty acid sucrose mono-acyl ester (SS) inhibited ceftibuten transport by BBMV similar to the action of polyoxyethylene sorbitans (Tweens), while fatty acid sucrose polyacyl ester mixtures (F-160 and F-140) did not affect the drug transport by BBMV. SS but not F-160 and F-140 caused an increase in the anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH)- and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide (TMA-DPH)-labeled BBMV in a concentration-dependent manner. Thus, the uptake of ceftibuten by BBMV was strongly correlated with the lipid fluidity of BBMV, in the outer layer and in the inner hydrophobic regions; however, there was no strong correlation between the membrane lipid fluidity and the drug uptake by BBMV. The micelle size and the size distribution of F-160 and F-140 were larger and more widely dispersed, respectively, compared to those of SS and Tweens. These results suggest that the effects of fatty acid sucrose esters on ceftibuten transport by BBMV are related to the dispersion parameter of these pharmaceutical adjuvants.     

Topographical relationship between sucrase and leucine beta-naphthylamidase on the microvilli membrane of rabbit intestinal mucosal cells

The topographical relationship between sucrase [EC 3.2.1.26] and leucine beta-naphthylamidase (LNAase) on the microvilli membrane of rabbit small-intestinal mucosal cells was studied assuming that where enzymes with different antigenicities, A and B, are situated in close proximity on the surface of microvilli vesicles, the agglutination of vesicles by anti-A antibody is inhibited by the previous binding of monovalent fragments of anti-B antibody to enzyme B on the surface of vesicles. Like anti-sucrase antibody, anti-LNAase antibody quantitatively agglutinated microvilli vesicles. It inhibited the membrane-bound LNAase activity in the same manner as the detergent-solubilized activity. This inhibitory effect of anti-LNAase antibody was not interfered with by monovalent fragments of anti-sucrase antibody. However, the monovalent fragments inhibited vesicle agglutination by anti-LNAase antibody as well as by anti-sucrase antibody. These results indicate that LNAase is located on the outer surface of microvilli vesicles and suggest that LNAase and sucrase are situated in close proximity on the membrane surface of microvilli vesicles.     

Inhibitory effects of angiotensin-converting enzyme inhibitor on cefroxadine uptake by rabbit small intestinal brush border membrane vesicles

Effects of angiotensin-converting enzyme (ACE) inhibitors, captopril, enalapril maleate and quinapril, on the uptake of aminocephalosporin antibiotic, cefroxadine, by rabbit small intestinal brush border membrane vesicles were examined. These ACE inhibitors significantly inhibited the uptake of cefroxadine, which is transported by H+/dipeptide transporter in the membrane, in the order of captopril < enalapril < quinapril in the presence of an inward H+ gradient. Inhibitory effect of quinapril was more marked than that of aminocephalosporin cephradine, while in the absence of an inward H+ gradient inhibition by these ACE inhibitors was much less. Dixon plot analysis showed that the inhibition by enalapril and quinapril in the presence of an inward H+ gradient occurred in a competitive manner and estimated inhibition constants of these two drugs to be 5.3 mM and 0.46 mM, respectively. These results suggested the strong affinity of these ACE inhibitors, especially quinapril, on the H+/dipeptide transporter.     

Production of membrane vesicles by extrusion: size distribution, enzyme activity, and orientation of plasma membrane and chloroplast inner-envelope membrane vesicles

A new animal model of hyperlipidemia is being developed using the nonionic surfactant poloxamer 407 (P-407). We investigated the impact of pravastatin on P-407-induced hyperlipidemia. Twenty rats received P-407 300 mg intraperitoneally to induce hyperlipidemia, and 20 control rats received saline injection. Pravastatin was administered orally to an equal number of rats in both groups using three different regimens. A fourth group did not receive pravastatin. At 24 hours after injection, total cholesterol levels in two of the pravastatin groups were 28% and 34% lower than those in animals that did not receive pravastatin (p < or = 0.01). At 48 hours, triglyceride levels were significantly lower in all pravastatin groups (21-44%) versus animals not receiving pravastatin. Pravastatin diminished the effects of P-407 on lipoproteins. This new animal model may be useful in screening for investigational antihyperlipidemic agents.     

Effect of membrane surface potential on the uptake and the inhibition of cationic compounds in rat intestinal brush-border membrane vesicles and liposomes

The effect of membrane surface potential on the uptake of tryptamine, an organic cation, by rat intestinal brush-border membrane vesicles was investigated. In the presence of an inside-negative K(+)-diffusion potential, the manner of initial uptake of tryptamine appeared to be pH-dependent and the uptake in the acidic medium was lower than that in the neutral medium. Changes in surface potential of brush-border membrane vesicles were monitored using 8-anilino-1-naphthalenesulfonic acid (ANS) and the results suggested that the membrane surface potential (negative charge on the membrane surface) decreased in the acidic medium. A good correlation was observed between the K(+)-diffusion potential-dependent uptake of tryptamine and membrane surface potential monitored by ANS at various pH levels. The uptake of tryptamine by liposomes (large unilamellar vesicles), which contained various amounts of dipalmitoylphosphatidylserine (DPPS), was also examined. The uptake of tryptamine decreased with a decrease of DPPS content in the liposomes, and was correlated with the membrane surface potential monitored by ANS. Moreover, the effect of organic cations on the uptake of tryptamine by intestinal brush-border membrane vesicles was examined. The uptake of tryptamine was inhibited by tetracaine and imipramine. The inhibitory effect of these cations was well correlated with changes in the membrane surface potential in the presence of tetracaine or imipramine. These results suggest that the K(+)-diffusion potential-dependent uptake of tryptamine by intestinal brush-border membrane vesicles is affected by membrane surface potential, and the inhibition of tryptamine uptake originates in changes in the membrane surface potential caused by the organic cations.     

Interaction of glucose oxidase with phospholipid vesicles

The interactions between glucose oxidase and phospholipid vesicles were investigated. The investigations were carried on molecules adsorbed on the outer surfaces as well as entrapped in the interior of the vesicles . The adsorption of glucose oxidase on the surfaces of egg egg licithin vesicles, containing varying amounts of cholesterol and stearoylamine was measured by determining the free fraction of glucose oxidase detected in the filtrates. In general an enhancement of enzymic activity was observed upon interaction with the vesicles. The enhancement depends on the lipid composition of the vesicles and the surface concentration of the adsorbed glucose oxidase. It reached a maximal value at a surface concentration of 1.4-10(11) molecules/cm2 (approximately 7.1 - 10(4) A2/molecule) on pure phosphatidylcholine vesicles and about 6.5 - 10(10) molecules/cm2 (approximately 16 - 10(4) A2/molecule) when the vesicles contained cholesterol or cholesterol and stearoylamine. CD measurements indicated that the change in enzymic activity of the adsorbed glucose oxidase was accompanied by conformational modification of the enzyme. In order to entrap glucose oxidase into the vesicles, the lipid was sonicated in the presence of the enzyme. After removal of the free and adsorbed enzyme the amount of the entrapped enzyme was determined by measuring its activity after disintegration of the vesicles with Triton. The enzymic activity of the entrapped glucose oxidase served as a measure for the permeability of the bilayer membrane of the lipid vesicles to glucose. Addition of insulin to the suspension of vesicles containing the entrapped glucose oxidase increased the permeability of glucose by up to 9 - 10(-8) cm/s. This value is the lowest estimate based on the assumption that one glucose oxidase molecule was entrapped in every vesicle.     

p-aminohippurate uptake by syncytial microvillous membrane vesicles of human term placenta

The mechanism of uptake of p-aminohippurate (PAH) by syncytial microvillous membrane vesicles of human term placenta was investigated. Initial PAH uptake and efflux were increased in the presence of a pH-gradient and a Cl(-)-gradient, respectively. Forced negative and positive membrane potentials did not influence the uptake, which indicated that the transport is not electrogenic. The pH-dependent increase is probably the result of a higher rate of diffusion due to a lower degree of dissociation of PAH. Because several organic anions failed to transstimulate PAH uptake and FCCP did not decrease the uptake in the presence of an inwardly directed H(+)-gradient, ruling out a PAH/OH- antiport, an anion exchange system does not appear to be present in these membranes. Since electrogenicity and anion exchange seem not to be involved in the Cl(-)-dependent increase, an allosteric effect of Cl- on the transporter might be possible. Various organic anions were able to inhibit pH-stimulated PAH uptake significantly. Kinetic analysis of the probenecid sensitive part of uptake provided further evidence for mediated transport of PAH (Km = 7.4 +/- 2.6 mM and Vmax = 2.0 +/- 0.4 nmol/mg/15 s). Non-inhibitable diffusion accounted for the main part of total transport. Concentration dependent inhibition of PAH transport by probenecid showed a Ki of 2.5 +/- 0.9 mM. It is concluded that human placental syncytial microvillous membrane vesicles possess a low affinity transport mechanism for PAH with low specificity. The importance of this system, for placental excretion of anionic drugs, will depend on the intrasyncytial concentration of these drugs, caused by the transport across the basal membrane.     

Proton gradient-driven nickel uptake by vacuolar membrane vesicles of Saccharomyces cerevisiae

A vacuolar H+-ATPase-negative mutant of Saccharomyces cerevisiae was highly sensitive to nickel ion. Accumulation of nickel ion in the cells of this mutant of less than 60% of the value for the parent strain arrested growth, suggesting a role for this ATPase in sequestering nickel ion into vacuoles. An artificially imposed pH gradient (interior acid) induced transient nickel ion uptake by vacuolar membrane vesicles, which was inhibited by collapse of the pH difference but not of the membrane potential. Nickel ion transport into vacuoles in a pH gradient-dependent manner is thus important for its detoxification in yeast.     

Modulation of sodium-coupled uptake and membrane fluidity by cisplatin in renal proximal tubular cells in primary culture and brush-border membrane vesicles

The proximal tubule appears to be the main target for the adverse effects of cis-diamminedichloroplatinum (II) (cDDP). We evaluated the early effects of cDDP at concentrations (3 to 67 microM) lower that those which alter cell viability, on three apical transport systems and on the physical state of the brush border membrane (BBM) in rabbit proximal tubule (RPT) cells in primary culture. The maximal effect, corresponding to a 30% decrease in Na(+)-coupled uptake of phosphate (Pi) and alpha-methylglucopyranoside (MGP) and a twofold increase in Na(+)-coupled alanine uptake, was obtained at 17 microM (5 micrograms/ml) cDDP and occurred through a modification of their affinity. At this concentration, cDDP increased BBM fluidity and decreased the BBM cholesterol content by 28%, without increasing the permeability of tight junctions. To clarify the role of cDDP-induced increase in BBM fluidity on alterations of Na(+)-coupled uptake, these parameters were also investigated in BBM vesicles isolated from rabbit renal cortex directly exposed to cDDP. cDDP induced a concentration-dependent inhibition of Na(+)-coupled uptake of MGP, Pi and alanine in BBM vesicles from the renal cortex, associated with a decrease in protein sulfhydryl content, without modifying BBM fluidity. Our findings strongly suggest that the cDDP-induced increase in BBM fluidity in RPT cells results from an indirect mechanism, possibly an alteration of cholesterol metabolism, and did not play a major role in the cDDP-induced inhibition of Na+/Pi and Na+/glucose cotransport systems that may be mainly mediated through a direct chemical interaction with essential sulfhydryl groups of the transporters.     

Transmembrane movement of phosphatidylcholine in mitochondrial outer membrane vesicles

One of the steps in the import of phosphatidylcholine (PC) in mitochondria is transmembrane movement across the outer membrane. This process was investigated in vitro using isolated mitochondrial outer membrane vesicles (OMV) from rat liver. 14C-Labeled PC was introduced into the OMV from small unilamellar vesicles by a PC-specific transfer protein (PCTP). The membrane topology of the newly introduced PC was determined from its accessibility to phospholipase A2. Under conditions where the OMV stay intact, externally added phospholipase A2 is able to hydrolyze up to 50% of both the introduced [14C]PC and the endogenous PC. Pool size calculations showed that close to 100% of the PC in the OMV can be exchanged by PCTP. A back-exchange experiment revealed that the introduction of the labeled PC is reversible. The results demonstrate that newly introduced PC molecules readily equilibrate over both leaflets of the OMV membrane. The kinetics of the PCTP-mediated exchange process indicate that the t1/2 of the transmembrane movement at 30 degrees C is 2 min or less.     

Regulation of endogenous glucose production by glucose per se is impaired in type 2 diabetes mellitus

We examined the ability of an equivalent increase in circulating glucose concentrations to inhibit endogenous glucose production (EGP) and to stimulate glucose metabolism in patients with Type 2 diabetes mellitus (DM2). Somatostatin was infused in the presence of basal replacements of glucoregulatory hormones and plasma glucose was maintained either at 90 or 180 mg/dl. Overnight low-dose insulin was used to normalize the plasma glucose levels in DM2 before initiation of the study protocol. In the presence of identical and constant plasma insulin, glucagon, and growth hormone concentrations, a doubling of the plasma glucose levels inhibited EGP by 42% and stimulated peripheral glucose uptake by 69% in nondiabetic subjects. However, the same increment in the plasma glucose concentrations failed to lower EGP, and stimulated glucose uptake by only 49% in patients with DM2. The rate of glucose infusion required to maintain the same hyperglycemic plateau was 58% lower in DM2 than in nondiabetic individuals. Despite diminished rates of total glucose uptake during hyperglycemia, the ability of glucose per se (at basal insulin) to stimulate whole body glycogen synthesis (glucose uptake minus glycolysis) was comparable in DM2 and in nondiabetic subjects. To examine the mechanisms responsible for the lack of inhibition of EGP by hyperglycemia in DM2 we also assessed the rates of total glucose output (TGO), i.e., flux through glucose-6-phosphatase, and the rate of glucose cycling in a subgroup of the study subjects. In the nondiabetic group, hyperglycemia inhibited TGO by 35%, while glucose cycling did not change significantly. In DM2, neither TGO or glucose cycling was affected by hyperglycemia. The lack of increase in glucose cycling in the face of a doubling in circulating glucose concentrations suggested that hyperglycemia at basal insulin inhibits glucose-6-phosphatase activity in vivo. Conversely, the lack of increase in glucose cycling in the presence of hyperglycemia and unchanged TGO suggest that the increase in the plasma glucose concentration failed to enhance the flux through glucokinase in DM2. In summary, both lack of inhibition of EGP and diminished stimulation of glucose uptake contribute to impaired glucose effectiveness in DM2. The abilities of glucose at basal insulin to both increase the flux through glucokinase and to inhibit the flux through glucose-6-phosphatase are impaired in DM2. Conversely, glycogen synthesis is exquisitely sensitive to changes in plasma glucose in patients with DM2.     

Similar effects of cis-diamminedichloroplatinum(II) and cis-diammine-1,1-cyclobutanedicarboxylatoplatinum(II) on sodium-coupled glucose uptake in renal brush-border membrane vesicles

cis-Diamminedichloroplatinum(II) (cDDP) has been shown to interfere with reabsorption processes in renal tubular epithelia, leading to polyuria, magnesium and sodium wasting and glucosuria. cDDP inhibits the Na+-coupled uptake of methyl-alpha-D-glucopyranoside (MGP) in renal proximal tubular cells in primary culture. cis-Diammine-1,1-cyclobutane dicarboxylatoplatinum(II) (CBDCA) produces tubular injury qualitatively similar to that of cDDP with a reduced severity. CBDCA inhibits Na+-coupled MGP uptake in renal proximal tubular cells in primary culture at concentrations 20- to 30-times higher than those of cDDP. The Na+/glucose cotransport protein possesses sulphydryl groups (SH) essential for its activity. Platinum complexes have strong affinity for SH groups. We compared the direct effects of cDDP (0.04-1.0 mM) and CBDCA (1-30 mM) on Na+-coupled MGP uptake in rabbit renal brush-border membrane (BBM) vesicles. cDDP and CBDCA inhibited Na+-coupled MGP uptake in a concentration-dependent manner, mainly through a decrease in Vmax of the cotransport protein. These effects were associated with platinum binding to BBM and decreases in protein-bound SH groups. CBDCA altered Na+-coupled MGP uptake at concentrations 30-times higher than those of cDDP. When BBM vesicles were preincubated with cDDP or CBDCA, diethyldithiocarbamate (an antidote against cDDP-induced nephrotoxicity) partly restored Na+-coupled MGP uptake and reduced the amount of platinum bound to BBM, but did not restore protein-bound SH groups. These findings strongly suggest that the inhibition of Na+-coupled MGP uptake by cDDP and CBDCA is mainly mediated by direct chemical binding of platinum to essential SH groups of the cotransport protein but may also involve other nucleophilic groups, such as the SCH3 group of methionine residues.     

Ketone body transport in renal brush border membrane vesicles

Ketone body uptake by renal brush border vesicles has been investigated. Ketone bodies enter into the brush border vesicles by a carrier-mediated process. The uptake is dependent on an Na+ gradient ([Na+]outside>[Na+]inside) and is electroneutral. The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. A pH gradient (alkaline inside) also stimulates the ketone body uptake. Acetoacetate and 3-hydroxybutyrate share the same carrier as demonstrated by the accelerated exchange diffusion and mutual inhibitory effects.     

Chromium, glucose intolerance and diabetes

Myopathies, regardless of their varied etiologies, are associated with muscle damage and, often, other organ system involvement causing physical impairment. The resultant adverse impact on mobility, activities of daily living, communication, and cardiorespiratory fitness results in disability, handicap, and reduced quality of life. The extent of the functional impact depends on the type of myopathy and the extent of clinical involvement caused by it, duration of the disease, time to diagnosis and treatment, and rate of progression and response to medical management. The usefulness of rehabilitation in maintaining function in muscular dystrophy has been addressed in the literature for several decades. However, the need for and efficacy of specific rehabilitation interventions and assessment tools to measure function in inflammatory myopathy have just recently emerged this decade. Although studies are few in number, they are useful. More research is needed and should be encouraged. The overall goal of rehabilitation is to enhance function and quality of life.