Temperature dependence of D-glucose transport in reconstituted liposomes

Sodium-dependent D-glucose uptake into proteoliposomes reconstituted from dimyristoylphosphatidylcholine (DMPC) and hog kidney brush border membrane extract is strongly affected by temperature and the physical state of the membranes. This dependence is defined by a nonlinear Arrhenius plot with a break point at 23 degrees C, a temperature not significantly different from the phase transition temperature of the pure lipid (24 degrees C). The transport process is characterized by different activation energies: 35.1 kcal/mol below and 5.5 kcal/mol above the transition temperature. The shift in the break point for the D-glucose transport activity from 15 degrees C, in the brush border membranes, to 23 degrees C in the reconstituted system leads us to conclude that the lipids surrounding the sodium/D-glucose cotransport system can exchange readily with the bulk lipid used for reconstitution. The results thus provide no evidence for the presence of an annulus of specific lipids surrounding the transport system.

Mercury intoxication simulating amyotrophic lateral sclerosis

A 54-year-old man had a syndrome resembling amyotrophic lateral sclerosis after a brief but intense exposure to elemental mercury. The syndrome resolved as his urinary mercury levels fell. Mercury toxicity must be considered not only in individuals with recent anterior horn-cell dysfunction but also with otherwise unexplained peripheral neuropathy, tremor, ataxia, and a gamut of psychiatric symptoms including confusion and depression.

Synthesis of [3H]phlorizin and its binding behavior to renal brush-border membranes

Tetra- and tribromophlorizin have been synthesized under mild brominating conditions. With catalytic debromination in the presence of hydrogen or tritium gas, bromine atoms in the derivatives were completely substituted by hydrogen or tritium. The product was identical to the native phlorizin and was chemically pure. Tritiated phlorizin with extremely high specific radioactivity (45 Ci/mmol) was obtained when hydrogen gas was replaced by tritium gas. While the brominated compounds showed little inhibition of sodium D-glucose co-transport by isolated renal brush-border membranes. [3H]phlorizin had the same binding affinity to the brush-border membranes as native phlorizin and a Ki value of 1.2 microM for the sodium-dependent D-glucose transport. Binding studies performed using a flow-dialysis method resulted in 150 pmol of phlorizin-binding sites per milligram of membrane protein. This radioactive phlorizin can be a useful tool for determining D-glucose-(phlorizin) binding sites at a low phlorizin concentration in membranes, in nonvesicle forms such as collapsed membrane vesicles, and in purified protein fractions.

A kinetic assay for Na-K-ATPase activity in isolated renal proximal tubules

A kinetic assay system which provides reliable measurements of Na-K-ATPase activity on 0.2 to 0.5-mm segments of renal proximal convoluted tubules isolated from collagenase-digested renal cortical slices is described. The use of collagenase digestion provides higher values for Na-K-ATPase, possibly by making the enzyme more accessible to the reaction system. The advantages of a kinetic vs an endpoint assay include the ability to use the same tubule as its own reference for the determination of total, ouabain-sensitive, and ouabain-insensitive ATPase activity. In addition, it allows dose-response studies on the effect of inhibitors on ATPase activity in the same tubule segment.

Mechanism of hematuria in glomerular disease. An electron microscopic study in a case of diffuse membranous glomerulonephritis

From an electron-microscopic study in a case of diffuse membranous glomerulonephritis, we would like to propose a possible mechanism of hematuria in glomerular disease. There are several factors we should consider: (1) the deforming force of the red blood cell (RBC); (2) the deformability of the RBC; (3) the size of the gaps in the glomerular basement membrane (GBM), and (4) the thickness of the GBM. The deforming force is due to increased capillary pressure in the glomerulus that alters the contour of the RBCs. If these gaps are larger than 0.25 micron, the stretching and retracting force of the internal chamber of the GBM, combined with the capillary pulse, cause the deformed RBCs to pass through the gaps and proceed to the urinary space.

Synthesis of phlorizin derivatives and their inhibitory effect on the renal sodium/D-glucose cotransport system

To characterize further the Na+/D-glucose cotransport system in renal brush border membranes, phlorizin - a potent inhibitor of D-glucose transport - has been chemically modified without affecting the D-glucose moiety or changing the side groups that are essential for the binding of phlorizin to the Na+/D-glucose cotransport system. One series of chemical modifications involved the preparation of 3-nitrophlorizin and the subsequent catalytic reduction of the nitro compound to 3-aminophlorizin. From 3-aminophlorizin, 3-bromoacetamido-, 3-dansyl- and 3-azidophlorizin have been synthesized. In another approach, 3'-mercuryphlorizin was obtained by reaction of phlorizin with Hg(II) acetate. The phlorizin derivatives inhibit sodium-dependent but not sodium-independent D-glucose uptake by hog renal brush border membrane vesicles in the following order of potency: 3'-mercuryphlorizin = phlorizin greater than 3-aminophlorizin greater than 3-bromoacetamidophlorizin greater than 3-azidophlorizin greater than 3-nitrophlorizin greater than 3-dansylphlorizin. 3-Bromoacetamidophlorizin - a potential affinity label - also inhibits sodium-dependent but not sodium-independent phlorizin binding to brush border membranes. In addition, sodium-dependent phosphate and sodium-dependent alanine uptake are not affected by 3-bromoacetamidophlorizin. The results described above indicate that specific modifications of the phlorizin molecule at the A-ring or B-ring are possible that yield phlorizin derivatives with a high affinity and high specificity for the renal Na+/D-glucose cotransport system. Such compounds should be useful in future studies using affinity labeling (3-bromoacetamido- and 3-azidophlorizin) or fluorescent probes (3-dansylphlorizin).

Renal sodium-D-glucose cotransport system. Involvement of tyrosine residues in sodium-transporter interaction

Using brush-border membrane vesicles isolated from calf kidney cortex the effect of tyrosine-reactive reagents on sodium-dependent D-glucose transport was investigated. Treatment of the membranes for 60 min with NBD-Cl (7-chloro-4-nitrobenzo-2-oxa-1,3-diazole), N-acetylimidazole or tetranitromethane decreased D-glucose uptake 50, 70 and 40%, respectively. Tracer exchange experiments revealed that the inhibition of transport is due to a direct modification of the sodium-D-glucose cotransport system. The modification by NBD-Cl decreases the apparent Vmax of the transport system with respect to its interaction with sodium. In addition, the rate of inactivation of the transport system by NBD-Cl is reduced in the presence of high concentrations of sodium. The results indicate that tyrosine residues play an essential role in sodium-D-glucose cotransport and are probably involved in the binding and/or transport of sodium by the sodium-D-glucose cotransport system.

Lymphocyte studies in a patient with chronic polyradiculoneuropathy

We studied immunologic abnormalities in one patient with chronic polyradiculoneuropathy and the effects of immune suppression and plasmapheresis on the clinical course and immune abnormalities. Increased helper T cells and B cells with deficiency of T suppressor cells to B-cell but not to T-cell targets were detected. The patient's blood lymphocytes, but not the controls' lymphocytes, proliferated in vitro on culturing them with P2 antigen in the presence of the patient's CSF. Plasmapheresis combined with corticosteroid and azathioprine reversed the majority of immune abnormalities to normal but did not decrease the patient's lymphocyte-P2 proliferative response; nor did it improve clinical status.

Convulsive syncope in blood donors

Syncope with and without convulsion was studied in unselected blood donors in a community blood center. Convulsive syncope occurred in 0.03% of all blood donors and was more commonly observed when nursing personnel were alerted to its possible occurrence. It was more common in men. Although tonic extensor spasm was the most common convwithout convulsion was studied in unselected blood donors in a community blood center. Convulsive syncope occurred in 0.03% of all blood donors and was more commonly observed when nursing personnel were alerted to its possible occurrence. It was more common in men. Although tonic extensor spasm was the most common convwithout convulsion was studied in unselected blood donors in a community blood center. Convulsive syncope occurred in 0.03% of all blood donors and was more commonly observed when nursing personnel were alerted to its possible occurrence. It was more common in men. Although tonic extensor spasm was the most common convulsive movement, other complex convulsive phenomena occurred, some simulating epileptic seizure. No statistical difference in changes of pulse or blood pressure was found between subjects with convulsive versus nonconvulsive syncope. Similarly, no difference was found between subjects with tonic spasm and those with other convulsive phenomena, nor between those with "early" and those with "delayed" reactions. Marked individual variation may exist in the susceptibility of the central nervous system to ischemia. Some individuals appear to be predisposed to development of seizures in situations of global cerebral ischemia such as occur in hypotension and bradycardia.

Partial purification of hog kidney sodium-D-glucose cotransport system by affinity chromatography on a phlorizin polymer

A brush border membrane fraction isolated from hog kidney cortex was solubilized with 0.5% Triton X-100 and subjected to affinity chromatography on a phlorizin polymer. As demonstrated by transport studies with reconstituted proteoliposomes, the polymer adsorbs the sodium-dependent D-glucose transport system. The latter can be eluted from the polymer by 0.5 M D-glucose. The purified fraction contains 0.4% of the membrane protein extract and exhibits a 20--30-fold higher transport activity than the crude membrane extract. Other brush border membrane proteins such as alkaline phosphatase and aminopeptidase M are markedly reduced in the purified fraction. Thus, affinity chromatography on a phlorizin polymer is a suitable tool for the isolation of the sodium-glucose transport system present in brush border membranes.

The use of octyl beta-D-glucoside as detergent for hog kidney brush border membrane

Octyl beta-D-glucoside was synthetized from alpha-acetobromoglucose with an improved method yielding a very pure product with a sharp melting point (108-109 degrees C) and free of intermediate products as judged by IR and NMR spectra. The yield of the synthesis is 66% when referred to alpha-acetobromoglucose. The potency of this compound as a detergent on hog kidney brush border membranes was compared to the action of Triton X-100. Octyl glucoside preferentially extracts aminopeptidase M and gamma-glutamyltranspeptidase in a concentration-dependent manner. The more deeply imbedded membrane enzyme, alkaline phosphatase, was relatively resistent to the action of octyl glucoside. In contrast, Triton X-100 extracted all membrane proteins to about the same extent. Additionally it was found that octyl glucoside can be removed from membrane extracts by Biobead SM 2. The capacity of the beads is about 170 mg detergent/g of dry Biobead SM 2. Thus octyl glucoside seems to be a useful tool for solubilization and purification of brush border membranes proteins.

Ethanediol monoester hydrolysis by monoacylglycerol lipase of rat liver microsomes

The hydrolysis of long-chain monoester of ethanediol by rat,liver subcellular fractions was investigated in order to define the carboxylic acid ester hydrolase involved and to localize the enzymic activity. We found that with 1-O-hexadecanoyl [U-14C]ethanediol as substrate, hydrolytic activity was foremost associated with the rough microsomal fraction. The pH optimum occurred at 8.5. The apparent Km and V values were 6.5 . 10(-4) M and 13 mumol/h per mg microsomal protein, respectively. Enzymic activity was inhibited by p-chloromercuribenzoate and by diisopropylfluorophosphate, whereas NaF was less effective and CaCl2 did not affect apparent activity. Amongst a number of carboxylic acid esters tested as substrate, only long-chain 1-acyl and 2-acyl glycerols inhibited acyl diol hydrolysis competitively (Ki approximately 0.9 mM). It was concluded that long-chain monoesters of ethanediol are hydrolyzed by the monoacyl glycerol lipase system associated with the rat liver microsomal fraction. Because diol monoester is also utilized by the cholinephosphotransferase system of liver to form highly lytic acyl diol phosphocholines, efficient diol monoester hydrolysis by monoglyceride lipase may be a significant step in regulating acyl diol phosphocholine levels in biological systems.

Psychiatric symptoms with initiation of carbidopa-levodopa treatment

Two patients who had had no previous psychiatric symptoms became psychotic after their antiparkinsonism medication was changed from levodopa alone to a combination of levodopa and carbidopa, despite adherence to the appropriate and recommended dosage. Psychiatric symptoms disappeared after treatment with levodopa alone was resumed.

Diol lipids of rat liver. Quantitation and structural characteristics of neutral lipids and phospholipids derived from ethanediol, propanediols, and butanediols

Specific enzymatic and chemical degradation of neutral lipid and phospholipid fractions from rat liver revealed the presence of novel types of lipid metabolites bearing a short-chain diol backbone. Diol-derived lecithin and cephalin analogs were readily cleaved by phospholipase C (EC 3.1.4.3) from Bacillus cereus, although the cephalin analogs required "carrier" lecithin to sustain hydrolysis. The products of phosphilipase hydrolyses as well as the neutral lipid fractions were subjected to alkaline and acidic methanolysis, and constituent short-chain diols were analyzed as long-chain cyclic acetals. Gas chromatographymass spectrometry confirmed that 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, and 1,3 butanediol can form the polyol backbone of neutral lipids and phospholipids. [1,1,2,2-2H]Ethanediol monohexadecanoate, dihexadecanoate, hexadecanoylphosphorylcholine, hexadecanoylphosphorylethanolamine were synthesized chemically and served as internal standards to assure accurate quantitation of the low levels of diol lipids (350 mug/g ot total lipid) present in rat liver.