HEXOSE INHIBITION OF AMINO ACID UPTAKE IN THE RAT-KIDNEY-CORTEX SLICE

DNA and other strands: the making of a human geneticist

This article--a mini-memoir--focuses on the first half of my half-century-long career as a human geneticist: its accidental beginnings; its early bad and then good fortunes at the National Institutes of Health; its serendipitous successes and career-making scientific productivity at Yale; and its incalculable fortuity in the form of the large number of talented and resourceful mentors, colleagues, postdoctoral fellows, graduate students, and technicians who worked with me. These years acted as a launchpad for positions of visibility and leadership that followed them. My personal odyssey, which began in Madison, Wisconsin, and meandered with no fixed plan to New York, Bethesda, New Haven, and Princeton, has offered me life views as a human and medical geneticist that are panoramic, splendid, and indelible. I doubt that many people have been as fortunate as I have been in the professional life I have lived--and continue to live.

A physiological replacement for polyvinylpyrrolidone (PVP) in assisted reproductive technology

The technique of intracytoplasmic sperm injection (ICSI) requires mechanical immobilization of the sperm that are to be injected; damage thus caused to the sperm membrane is considered to be necessary to activate the sperm for fertilization. Mechanical immobilization and the injection procedure are facilitated by introducing the sperm into a viscous medium that will hinder motility: a solution of polyvinylpyrrolidone (PVP) has been used successfully for this purpose. PVP is an artificial polymer, which has been regarded as chemically inert, although adverse effects have been reported as a result of its use both in vivo and in vitro. Therefore, the use of hyaluronate, the natural component of the extracellular matrix of the cumulus-oocyte complex, was investigated as a replacement for PVP during ICSI. A solution of hyaluronate was found to be as effective as PVP in facilitating the injection procedure, its effect on sperm motility was readily reversible, and its use did not affect the outcome of the treatment cycles in terms of fertilization, pregnancy and live birth rates. Every attempt should be made to eliminate artificial factors in assisted reproductive procedures. Hyaluronate, a natural and readily degradable glycosaminoglycan can be used as a substitute for the artificial PVP polymer without jeopardising the outcome of the treatment cycle.

Abnormal amino acid concentrations in plasma and urine of experimentally diabetic dogs

Free amino acid concentrations have been determined in plasma and urine of nonketotic, severely diabetic dogs and age-matched normal controls. Plasma from fasted (as well as fed) diabetics contained supranormal concentrations of several amino acids, including the branched-chain amino acids. In contrast to other species, however, the concentration of only one plasma amino acid (tryptophan) was subnormal in fasted diabetic dogs. Urine collected at the same time showed that the excretion of most amino acids was not abnormal in diabetes. Urinary concentrations of some amino acids were not abnormal despite supranormal levels in plasma. Nevertheless, eight of the 21 amino acids studied reached concentrations significantly greater than normal in the urine of diabetic dogs. Six of the eight amino acids (arginine, histidine, phenylalanine, tyrosine, tryptophan, glutamic acid) showed elevated concentrations in urine even though their plasma concentrations were not elevated. The observed disturbance in the urine/plasma ratio of certain amino acids suggests a possible defect in the renal handling of amino acids in diabetes.

On the ability of galactose to influence hexose and amino acid uptake by isolated rat brain capillaries

The uptake of glucose, 2-deoxyglucose, proline, methionine, and alpha-methylamino isobutyric acid was studied in brain capillaries preincubated with 50 mM galactose either in vitro or isolated from galactose-fed rats. The uptake was not decreased in both cases. The linear rate of glucose oxidation by capillaries was also not altered by preincubation with galactose.

Familial Fanconi syndrome with malabsorption and galactose intolerance, normal kinase and transferase activity. A report on two siblings

Two siblings of Turkish-Assyrian extraction, whose parents were first cousins, had poor appetite, slow weight gain and retarded psychomotor development. When given milk the galactose concentration in blood increased. An oral galactose load showed a markedly reduced capacity to metabolize galactose. Fanconi syndrome was present as in classical galactosemia. A galactose-free diet reduced the aminoaciduria but did not normalize the renal tubular function nor the children's general condition. Galactokinase and galactose-1-phosphate uridyltransferase activities in red blood cells were normal. The physical appearance of the children (sparse subcutaneous fat, thin extremities and distended abdomen) and the results of vitamin A and xylose absorption tests, were in accordance with a malabsorption condition. Glucose, however, seemed to be absorbed normally from the gut. There was no evidence of primary liver disease. Since the condition did not normalize with a galactose-free diet, an enzyme defect of galactose metabolism is unlikely. Instead, a more general transport defect with autosomal recessive inheritance is proposed.

Influx of gamma-aminobutyric acid and alpha-aminoisobutyric acid into mouse cerebrum slices incubated in a pyruvate medium with or without added glucose or glucose analogues compared with influx from a glucose medium

Concentrative influx of gamma-aminobutyric acid (GABA) and alpha-amino-isobutyric acid (AIB) into incubated mouse cerebrum slices is decreased when pyruvate is substituted for glucose. Influx of GABA from pyruvate medium is not increased by presence of glucose, 2-deoxy-D-glucose (2-DOG), or 3-O-methyl-D-glucose (3-O-MeG). Influx of AIB is restored to the rate from glucose medium if 2-DOG is present initially, but is not restored if 2-DOG is added with AIB. Influx is not restored if 3-O-MeG is present initially, but is restored if 3-O-MeG is added with AIB. Influx is restored if glucose is present initially or is added with AIB.

Carbohydrate effects of amino acid transport by Trypanosoma equiperdum

Uptake of 14C-labeled alanine, glutamate, lysine, methionine, proline, and phenylalanine by Trypanosoma equiperdum during 2-minute incubations occurred by diffusion and membrane-mediated processes. Amino acid metabolism was not detected by paper chromatography of trypanosome extracts. Most of 18 carbohydrates tested for ability to alter amino acid transport neither changed nor significantly inhibited transport. Glucose, however, stimulated glutamate, lysine and proline transport; fructose stimulated lysine uptake and 2-deoxy-D-glucose increased phenylalanine and methionine absorption. No evidence was found that the carbohydrates acted by binding to amino acid transport "sites." Glucose inhibition of alanine, phenylalanine, and methionine uptake was linked to glycolysis. The rapid formation of alanine form glucose stimulated alanine release and, when glycolysis was blocked, glucose no longer inhibited alanine transport. Methionine and phenylalanine release was also stimulated by glucose. Glucose changed the ability of lysine, glutamate, and proline to inhibit each others' uptake, indicating that certain amino acids are preferentially absorbed by respiring cells. Analysis of free pool amino acid levels suggested that some amino acid transport systems in T. equiperdum are linked in such a way to glycolysis as to control the cell concentrations of these amino acids.

Inhibition of cellular transport processes by 5-thio-D-glucopyranose

5-Thio-d-glucopyranose, the nearest analogue of normal d-glucose, which is proving a useful tool in examinations of d-glucose biochemistry, affects active and facilitated-diffusion transport processes. 5-Thio-d-glucose is readily transported in rabbit kidney-cortex slices and reaches a tissue/medium ratio of 6.5 within 40min. The sulphur analogue shows typical saturation kinetics with a K(m) value of 2.4mm and V(max.) value of 70mumol/h per g of cell water. Uptake of 5-thio-d-glucose is phlorrhizin-sensitive, Na(+)-dependent and energy-dependent. d-Galactose and methyl alpha-d-glucopyranoside transport is competitively inhibited by 5-thio-d-glucose with K(i) values of 4.8 and 9.7mm respectively. 5-Thio-d-glucose thus shows all of the characteristics of active transport in kidney cortex. Transport of neutral amino acids in rat kidney cortex is inhibited by 5-thio-d-glucose. Thus 5.6mm-5-thio-d-glucose causes a 25-30% inhibition of the transport of glycine and the non-metabolized amino acids cycloleucine and alpha-aminoisobutyric acid. 5-Thio-d-glucose is freely taken up by the facilitated-diffusion transport system in rat diaphragm muscle. The sulphur analogue inhibits the transport of d-xylose in this tissue but has no effect on the uptake of d-arabinose. It is concluded that the ring heteroatom is not an effector of binding in the transport processes examined and causes no important alteration in the conformation of the sugar. The diabetogenic action produced by 5-thio-d-glucose is due, in part, to the ability of the analogue to interfere with cellular transport processes that use d-glucose.

Transport and metabolism of galactose in rat kidney cortex

1. Analysis of transport of d-galactose was complicated by metabolism of the compound but appeared to have two components: a substrate-saturable component and a diffusion component. At low substrate concentration (<1mm) active transport was observed. Accumulation of galactose was largely independent of Na(+) concentration. The apparent K(m) for this component was 0.2mm. At substrate concentrations above 1mm the active transport system appeared saturated and further increases in substrate concentration resulted in a linear increase in the rate of galactose accumulation, but no concentration gradient was formed. 2. d-[1-(14)C]Galactose (2mm) was metabolized to (14)CO(2) by rat kidney-cortex slices incubated at 37 degrees C, at the rate of 68nmol/h per 100mg of tissue. 3. Intracellular components from such incubations were separated into a neutral fraction, the only major labelled component being galactose, and a phosphorylated fraction. 4. Phosphorylated metabolites found in galactose-incubated slices increased with increasing substrate concentration and achieved a limiting value of 0.42mm after 60min of incubation. 5. Galactose uptake was inhibited by anaerobiosis, dinitrophenol and phlorrhizin. 6. Methyl alpha-d-glucoside and d-glucose partially inhibited galactose uptake only at ratios of 100:1. 7. The presence of pyruvate did not decrease galactose metabolism although it did decrease production of (14)CO(2) from [1-(14)C]galactose. Gluconeogenesis occurred in the presence of pyruvate and (14)C from galactose was found in glucose. 8. Rat kidney-cortex slices metabolized 2mm-[1-(14)C]galactonate to (14)CO(2) at a rate of 20nmol/h per 100mg of tissue.

Separate transport systems for sugars and amino acids in developing rat kidney cortex

The ability of renal cortical slices of newborn and young rats to accumulate a nonmetabolizable sugar, alpha-methylglucoside, is slight and does not reach adult capacity until 25 days of age. However, a rudimentary sugar transport system is present, as indicated by a further decrease in accumulation in the presence of phlorizin or absence of sodium ion.Amino acid uptake in immature kidney tissue is not deficient; on the contrary, the tissue took up and concentrated more glycine and lysine than adult tissue. Decreased amino acid efflux from the immature cells appears to be the explanation. Concentration dependence of amino acid uptake was the same in 5-day-old and adult tissue. These differences between the transport characteristics of a model sugar and representative amino acids during development indicate separate transport systems for the two types of substrate.

Transport of monosaccharides in kidney-cortex cells

1. The aerobic accumulation of various monosaccharides in slices of rabbit kidney cortex at 25 degrees was studied. 2. d-Fructose and alpha-methyl d-glucoside were readily accumulated against their concentration gradient by a phlorrhizin-sensitive Na(+)-dependent active transport. In the absence of external Na(+) the maximal rate of alpha-methyl glucoside transport was decreased tenfold, the K(m) of entry into the cells (8.2mm) not being affected. Phlorrhizin and d-galactose inhibited the entry of alpha-methyl glucoside also in the absence of external Na(+). 3. d-Xylose, 6-deoxy-d-glucose and 6-deoxy-d-galactose were poorly accumulated ([S](i)/[S](o) ratios slightly above 1.0); this transport was inhibited by phlorrhizin and by the absence of Na(+). 4. 3-O-Methyl-d-glucose, d-arabinose and l-arabinose were not actively transported, [S](i)/[S](o) ratios never exceeding 1.0. 5. 2-Deoxy-d-glucose and 2-deoxy-d-galactose were readily accumulated against a high concentration gradient, this transport being Na(+)-independent and only slightly sensitive to phlorrhizin. External Na(+) was not required for an inhibitory action of phlorrhizin and d-galactose on the entry of 2-deoxy-d-galactose into the cells. 6. Interference for entry into the cells between the following saccharides was found: d-galactose inhibited alpha-methyl d-glucoside transport; d-xylose entry was inhibited by d-glucose; d-galactose transport was inhibited by d-xylose; a mutual interference between d-galactose and its 2-deoxy analogue was found. 7. It is concluded that d-glucose, d-galactose, alpha-methyl d-glucoside, d-xylose and possibly also some other monosaccharides share a common active transport system. 8. The specificity of the Na(+)-dependent phlorrhizin-sensitive active transport system for monosaccharides in kidney-cortex cells differs from that in intestinal epithelial cells.