Hexose transport in plasma membrane vesicles of rat myoblast L6

To determine the molecular mechanism of hexose transport in rat myoblasts, transport studies were carried out with purified plasma membrane vesicles. Rat myoblasts were homogenized and fractionated by differential and sucrose gradient centrifugation. Six different fractions were obtained. Studies with marker enzymes revealed that two fractions (A and B) were composed of only plasma membrane. These two fractions differed considerably in their physical properties. Fraction A was composed of large multilaminated vesicles, with an intravesicular volume of 50 μL/mg protein, whereas fraction B was composed of membrane fragments and much smaller vesicles, with an intravesicular volume of 7 μL/mg protein. Based on the response of the ouabain-sensitive Na+,K+-ATPase activity to sodium dodecyl sulfate and ionophore treatments, it seemed likely that fraction A was composed of a significant amount of sealed right-side-out vesicles, whereas fraction B was composed of mainly membrane sheets or leaky vesicles. The initial rate of hexose influx into the membrane vesicles was determined by the flow dialysis technique. The optimal conditions for 2-deoxyglucose (2-DG) uptake into the plasma membrane vesicles were either 50 mM phosphate buffer or 10 mM 2-(N-2-hydroxyethylpiperazin-N′-yl)ethanesulfonic acid buffer at pH 7.0. In the presence of 500 μM 2-DG, the initial rates of 2-DG influx were 295 and 49 nmol/min per milligram protein for fractions A and B, respectively. In other words, after 1 min of incubation, the intravesicular concentration of 2-DG was around 6 mM, about 10 times the extravesicular concentration. D-Glucose was taken up to a similar extent (333 nmol/min per milligram protein), whereas L-glucose only equilibrated across the plasma membrane. Analysis of the fate of 2-DG revealed that the substrate was not phosphorylated upon incubation with the vesicles. Transport activity can be abolished either by disruption of the membrane vesicles or by reduction of the electrical potential across the membrane.

Regulation of insulin binding and stimulation of sugar transport in cultured human fibroblasts by sugar levels in the culture medium

Studies were carried out on cultures of human skin fibroblasts to explore the effects of culture medium glucose levels on insulin binding and action. Cell cultures in 5.55 mM glucose-containing medium depleted their medium glucose within 3 days, and at that time exhibited elevated deoxy-D-glucose (2-DG) transport (84% greater than control cultures fed 22.2 mM glucose) and failure of insulin to stimulate 2-DG transport (an insulin:control transport ratio of 1.02). There was also a significant negative correlation between basal 2-DG transport and insulin binding (r = -0.621; n = 29; P less than 0.01), while insulin binding exhibited a significant positive correlation with insulin action (r = 0.816; n = 12; P less than 0.01). Glucose starvation of cultures for 18 h resulted in several changes: a 49% decrease in specific 125I-insulin binding due to a reduction in binding capacity; elevated basal 2-DG transport; and an absence of insulin stimulation of 2-DG transport. Exposure to increasing concentrations of glucose for 18 h led to a glucose concentration-dependent increase in specific insulin binding. Additionally, the various changes in the glucose-starved group were reversed after as little as 6 h of glucose refeeding. The results indicate that basal sugar transport, and insulin binding and action can be regulated by the amount of glucose in the medium.

2-Deoxyglucose uptake in the thalamus of awake rats after neocortical ablations

Local, temporary or permanent depressions and elevations in 2-deoxy[14C]glucose (2-DG) uptake were observed in the brains of unanesthetized, freely moving rats that 3 days to 1 year earlier had sustained large unilateral posterior neocortical ablations. Some of the differences in metabolic activity between the normal and damaged hemispheres, in both cortical and subcortical regions, were attributed to cell death and gliosis, and surgical trauma. In addition, it appeared that certain metabolic changes provided a physiologic correlate of diaschisis, a temporary impairment in function which von Monakow hypothesized to occur in neurons denervated by a lesion. We concluded that the 2-DG technique is a useful tool for examining the widespread effects of brain damage, and that when employed in the manner exemplified by this and a previous study, the technique can disentangle the changes in neural activity which occur after brain damage from the changes in glial activity which accompany them.

Stimulation of hexose uptake in rat thymic lymphocytes by phorbol ester. A role for Ca2+ and Na+/H+ exchange?

The tumor promoter 12-0-tetradecanoyl phorbol-13-acetate (TPA) stimulates hexose uptake into rat thymocytes. This study explores two possible messengers of this stimulation: changes in cytosolic [Ca2+], and activation of the Na+/H+ antiport. The cytosolic level of Ca2+, determined by the fluorescence of quin-2, was elevated by TPA, and this rise required extracellular Ca2+. In contrast, stimulation of hexose uptake was still observed in Ca2+ -free media even when cytoplasmic [Ca2+] was buffered with quin-2. TPA also raised the cytoplasmic pH, presumably through activation of the Na+/H+ exchange. However, replacement of extracellular Na+ by N-methylglucamine+ or choline+ which prevents the cytoplasmic alkanization did not prevent stimulation of hexose uptake by TPA. Moreover, amiloride, at concentrations that inhibit Na+/H+ exchange in these cells, did not interfere with stimulation of hexose uptake by TPA. In conclusion, stimulation of hexose uptake by phorbol ester in rat thymocytes does not appear to be mediated by changes in cytosolic free Ca2+ or in the activity of the Na+/H+ antiport.

Insulin binds to specific receptors and stimulates 2-deoxy-D-glucose uptake in cultured glial cells from rat brain

The kinetics of 125I-insulin binding and physiological activity of insulin on glial cells cultured from brains of 1-day-old rats have been studied. Binding of 125I-insulin to cultured glial cells was specific, reversible, and time-dependent. Porcine and chicken insulin competed equally for 125I-insulin binding while other hormones or insulin analogs competed in proportion to their insulin-like biological activity. Incubation of glial cultures with insulin resulted in a time- and dose-dependent stimulation of 2-deoxy-D-glucose uptake. Maximal stimulation (190% of control) was observed with 18 nM insulin, and 0.1 nM insulin caused half-maximum effect. The stimulatory effect of insulin on 2-deoxy-D-glucose uptake was due to its effect on Vmax without affecting the Km. These observations suggest that insulin stimulates glucose uptake in glial cells cultured from rat brain, the effect mediated by insulin specific receptors.

Effect of mating on the metabolic activity of the brain and pituitary gland assessed by [14C]2-deoxyglucose in a reflex ovulator, the vole (Microtus agrestis)

The neural pathways involved in reflex ovulation in the vole (Microtus agrestis) have been investigated with the [14C]2-deoxyglucose (2-DG) method. Female voles were injected i.p. with 2-DG and either not mated, sham-mated (mounted by males by vagina was taped) or mated for a period of 45 min after the injection, after which the animals were decapitated. The brain was processed for autoradiography and the relative metabolic activities (rma) of selected areas of the brain and pituitary gland were determined. The plasma separated from trunk blood was assayed for the concentration of luteinizing hormone (LH). The lordosis quotients (LQ) were (mean +/- S.E.M.) 81 +/- 8 (n = 5) in mated compared with 47 +/- 8 (n = 5) in sham-mated voles. The rma of the midbrain central grey (CG) and reticular formation (RF) were significantly greater in mated and sham-mated voles compared with the values in unmated voles. There were no other between-group differences in the rma of the other 28 areas of the brain or pituitary gland studied in spite of the fact the plasma LH concentration in mated voles was 36.9 +/- 9.6 ng NIH-LH-S18/ml compared with undetectable (less than 2.5 ng/ml) values in all the sham-mated and unmated animals. These results show that in the vole increased metabolic activity of the CG and RF is associated with lordosis, but that the reflex release of LH is not accompanied by any significant change in the metabolic activity of the brain or the pituitary gland.

Effects of cholesterol autoxidation derivatives on hexose transport in cultured aortic smooth muscle cells

Several cholesterol autoxidation derivatives known to be cytotoxic to arterial smooth muscle cells both in vivo and in vitro were shown to inhibit hexose transport in these cells in culture. Cholestane-3 beta, 5 alpha, 6 beta-triol was the most potent inhibitory sterol. The rapid onset of inhibition (15 min) and the reversibility of the effect upon removal of the sterol from the tissue culture medium suggests that the effect may be due to incorporation of the sterol into the plasma membrane. 25-Hydroxycholesterol, a potent inhibitor of sterol biosynthesis in cultured arterial smooth muscle cells, did not affect hexose transport up to 8 hr of incubation. The cytotoxic effect of 25-hydroxycholesterol, therefore, may be a consequence of the reduced sterol biosynthesis caused by this sterol.

Inhibitory contours in the inferior colliculus as revealed by the 2-deoxyglucose method

2-Deoxyglucose experiments were carried out during which tone bursts were presented to one ear of cats, while white noise bursts were presented to the other ear. Autoradiography revealed that the tones had produced clear bands of reduced labelling in the ipsilateral inferior colliculus, in addition to the expected band of increased labelling in the contralateral inferior colliculus. The positions of the bands or contours appeared to be organized tonotopically into iso-frequency inhibitory contours.

Attempts to combine 2-deoxyglucose autoradiography and tyrosine hydroxylase immunohistochemistry

The possibilities were analysed to combine the 2-deoxyglucose technique and indirect immunofluorescence histochemistry using tyrosine hydroxylase antiserum, with the aim to study functional activity in immunohistochemically characterized single neurons. Since the product measured with the 2-deoxyglucose method is water soluble and since immunohistochemistry requires that sections repeatedly run through aqueous media, the 2-deoxyglucose method was carried out before fixation and immunohistochemistry. The routine rapid thaw-mounting at + 60 degrees C of sections for 2-deoxyglucose autoradiography was found not to be compatible with immunohistochemistry. Instead a new mounting technique based on "gluing" the sections on to the object slide with a mixture of a standard mounting medium (Permount) and xylene was used to avoid diffusion at this stage. Two procedures were outlined, both starting with unfixed brains cut on a cryostat. In Method I autoradiographic sheet film was used. After autoradiographic exposure, the section was immersion-fixed in formalin, processed for immunohistochemistry, analysed and photographed in a fluorescence microscope and the results compared with the autoradiographic distribution patterns on the film. However, only the low resolution of the routine 2-deoxyglucose technique was obtained, which did not allow analysis of activity in single cells. In Method II, liquid emulsion applied by the loop technique was used. After exposure, autoradiographic developing and fixation, dehydration, mounting, analysis and photography of autoradiographs in the light microscope, the cover-slip was removed, the sections rehydrated and processed for indirect immunofluorescence histochemistry. With this procedure single autoradiographically labeled cells were observed, some of which contained tyrosine hydroxylase. Thus, with Method II it may in the future be possible to monitor functional activity in single immunohistochemically identified neuronal cell bodies. In order to obtain a useful and reliable method for this purpose, however, further extensive work with regard to, for example, quantification will be required.

Local cerebral glucose utilization in systemic acidosis

Cerebral glucose metabolism (CMRglu) is decreased during acute and prolonged hypercapnic acidosis and during prolonged metabolic (HCl) acidosis; it is increased in acute (hypocapnic) metabolic acidosis and is not changed in acute isocapnic metabolic acidosis. The alteration in CMRglu can be explained by the changes occurring in intracerebral pH under these experimental conditions. In pontine gray matter, n. tractus solitarii, and n. ambiguus, three structures participating in the neuronal regulation of ventilation, local CMRglu is increased in all acidotic groups, suggesting coupling of function and metabolism at the local level during acidosis-induced hyperventilation.

2-Deoxyglucose incorporation into rat brain glycogen during measurement of local cerebral glucose utilization by the 2-deoxyglucose method

The incorporation of 14C into glycogen in rat brain has been measured under the same conditions that exist during the measurement of local cerebral glucose utilization by the autoradiographic 2-[14C]deoxyglucose method. The results demonstrate that approximately 2% of the total 14C in brain 45 min after the pulse of 2-[14C]deoxyglucose is contained in the glycogen portion, and, in fact, incorporated into alpha-1-4 and alpha-1-6 deoxyglucosyl linkages. When the brain is removed by dissection, as is routinely done in the course of the procedure of the 2-[14C]deoxyglucose method to preserve the structure of the brain for autoradiography, the portion of total brain 14C contained in glycogen falls to less than 1%, presumably because of postmortem glycogenolysis which restores much of the label to deoxyglucose-phosphates. In any case, the incorporation of the 14C into glycogen is of no consequence to the validity of the autoradiographic deoxyglucose method, not because of its small magnitude, but because 2-[14C]deoxyglucose is incorporated into glycogen via [14C]deoxyglucose-6-phosphate, and the label in glycogen represents, therefore, an additional "trapped" product of deoxyglucose phosphorylation by hexokinase. With the autoradiographic 2-[14C]deoxyglucose method, in which only total 14C concentration in the brain tissue is measured by quantitative autoradiography, it is essential that all the labeled products derived directly or indirectly from [14C]deoxyglucose phosphorylation by hexokinase be retained in the tissue; their chemical identity is of no significance.

Classical conditioning enhances auditory 2-deoxyglucose patterns in the inferior colliculus

The [14C]2-deoxyglucose (2-DG) method in conjunction with a heart rate conditioning paradigm was used to investigate whether associative pavlovian conditioning of an acoustic stimulus (CS) with an aversive reticular stimulus (US) would result in a learning-induced metabolic response within the rat inferior colliculus (IC). The data show that: (1) the arousal level of the animal can result in a sensitization of the IC to subsequent auditory stimuli, and (2) the overlapping area of spatial representation of US and CS within the IC selectively develops an enhanced metabolic response during training and as a result of learning. Our results support the conclusion that within the same neuronal space of the IC there is representation not only of the physical parameters of a stimulus but also of its learned behavioral significance.

'Abnormality of 2-deoxyglucose uptake kinetics in fibroblasts at low concentrations

2-deoxyglucose uptake rates at low sugar concentrations (less than 500 microM) appeared to be lower than those predicted by the Michaelis-Menten model which correctly described higher concentrations. This phenomenon which we will call concentration-dependent transport lag, was also observed for L-glucose uptake which suggest that this phenomenon is carrier-independent. A model involving the perimembrane space is developed which, for L-glucose, gives k1 = 0.931 +/- 0.072 X 10(-6) l X mg protein-1 X minute-1, k2 = 2.97 +/- 0.19 X 10(-7) l X mg protein-1 X minute-1 and So = 88,8 +/- 4,3 microM; where k1 is the diffusion constant in the cell membrane, k2 is the diffusion constant in the perimembrane space and So the sugar concentration required in the external medium in order to provide an équivalent sugar concentration in the transport carrier area.

Nicotinamide and other inhibitors of ADP-ribosylation block deoxyglucose uptake in cultured cells

Nicotinamide was shown to inhibit deoxyglucose uptake in three diverse differentiated cell lines. In 3T3-L1 fat cells, nicotinamide equally inhibited basal and insulin stimulated deoxyglucose uptake. Inhibition by nicotinamide was non-competitive. A variety of inhibitors of ADP-ribosylation blocked deoxyglucose uptake while some analogs with no activity against ADP-ribose synthetase also had little effect on deoxyglucose uptake. These findings should be taken into account when inhibitors of ADP-ribosylation are used with intact cells.

The effect of insulin and hydrocortisone on the in vivo tissue uptake of 2-deoxyglucose in mice

The purpose of this study was to assess the feasibility and limitations of using the uptake of 14C-2-deoxyglucose (14C-2DG) under nonsteady-state conditions in the conscious mouse as a screening model for detecting changes in glucose uptake. Male, Swiss--Webster mice were administered an i.v. dose of 2-deoxyglucose (2DG, 50-75 mg/kg) with 14C-2DG (20 microCi/kg, 44-66 microCi/mmole). The levels of 14C-2DG were measured in gastrocnemius muscle, retroperitoneal fat, liver, cerebral cortex, and blood. Insulin (2 U/kg) s.c. significantly reduced 2DG levels in blood and liver compared to saline controls but significantly increased 2DG levels in muscle and fat. There was no effect on cerebral cortex 2DG uptake. Hydrocortisone (HC) treatment (300 mg/kg, i.p.) significantly reduced brain and muscle 2DG uptake. The effect of HC on brain 2DG levels may be caused by an indirect effect since determination of the 14C-sorbitol space indicated that HC reduced sorbitol levels in the brain when compared to saline controls, a reduction not detected in muscle. The limitations of the model seem to involve the brain and liver. Increasing glucose concentrations (i.v. glucose challenge) lead to decreased 2DG brain levels. It also appears that 2DG may not be reflecting glucose assimilation in the liver. However, it appears that the in vivo 2DG uptake model is a useful screening method for detecting changes in 2DG assimilation in fat and muscle following drug treatment.

Cochlear deoxyglucose uptake: relationship to stimulus intensity

The relationship between stimulus intensity and the uptake of 2-deoxyglucose (2-DG) in the cochlea of the gerbil was studied using an autoradiographic technique. In silence, incorporation of labeled 2-DG into stria vascularis and the spiral ligament was significantly higher than for other inner ear structures. With increasing intensity of noise exposure, 2-DG uptake in the spiral ganglion and VIIIth nerve increased dramatically when compared to the lateral wall structures. In contrast, relative 2-DG uptake in the organ of Corti was much less affected by noise exposure. Only at 105 dB SPL, the highest intensity tested, was a modest but statistically significant increase observed in the sensory epithelium. The small change in relative 2-DG uptake observed in the organ of Corti during acoustic stimulation is consistent with Davis' (1965: Quant. Biol. 30, 181-190) battery model of the cochlear transduction process. Alternatively, a larger change may have occurred, but been restricted to a small portion of the epithelium, such as one or both populations of hair cells.

Fatty acid mobilization to 2-deoxyglucose is blocked by globus pallidus lesions

Lesions of the lateral hypothalamus or discrete bilateral transections on the lateral border of the lateral hypothalamus disrupt the mobilization of metabolic fuels to intraperitoneal administration of the glucose analog 2-deoxyglucose. To better define the pathways involved in these responses, the effects of globus pallidus lesions on body fuel mobilization were investigated. Globus pallidus lesions blocked the increase in plasma free fatty acids normally caused by 2-deoxyglucose, but did not diminish the concomitant hyperglycemia. The data indicate that a pathway running through the globus pallidus, crossing the dorsoanterolateral hypothalamic border, and turning caudally in the dorsolateral hypothalamus is important in the immediate release of free fatty acids following 2-deoxyglucose administration.

Enhanced neural response to familiar olfactory cues

Norway rat pups have an enhanced olfactory bulb response to a familiar odor. A specific complex of glomeruli showed increased carbon-14-labeled 2-deoxy-D-glucose uptake in response to peppermint odor in 19-day-old pups exposed to peppermint on days 1 to 18 after birth, relative to control pups that had been exposed to clean air. The increased activity was not due to increased respiration of the familiar odor.

Effects of vanadate on intracellular Ca2+ redistribution and hexose transport across plasma membrane in cultured mouse fibroblasts

The effects of vanadate on intracellular Ca2+ sequestration and hexose transport were studied in Swiss 3T3 cells. Vanadate inhibited ATP-dependent Ca2+ uptake by saponin-permeabilized Swiss 3T3 cells at 10(-5) and 10(-7) M Ca2+ at which the Ca2+ uptake was sensitive and insensitive to oligomycin plus antimycin A, respectively. On the other hand, vanadate stimulated 2-deoxy-D-glucose (2DG) uptake in a dose- and time-dependent way. The stimulation of 2DG uptake by vanadate was inhibited by EGTA plus A23187 and the inhibition was reversed by Ca2+ restoration. These results suggest that an increase in cytosolic Ca2+ by inhibition of intracellular ATP-dependent Ca2+ sequestration by vanadate results in the stimulation of hexose transport in Swiss 3T3 cells.

Identification of a glycosidase activity with apparent specificity for 2-deoxy-D-glucose in glycosidic linkage

2-Deoxy-D-glucose (dGlc) is a carbohydrate with significant activity as an inhibitor of glucose metabolism and as a precursor in the synthesis of glycosylated macromolecules; several of the enzymes associated with its metabolism remain uncharacterized. In the present report, the partial purification and some of the properties of a mammalian enzyme that appears to be relatively specific for the hydrolysis of dGlc bound in glycosidic linkage is described. The physiological function of this enzymatic activity is unknown. In addition, dGlc has been shown to be taken up by HTC cells in culture and incorporated into macromolecular bound form, both as dGlc and as 2-deoxygalactose which is formed from dGlc.

A simplified method for computerized densitometry of complex shapes in 2-deoxyglucose autoradiographs

A simple, computerized densitometer is described which can be used to measure densities of photographic prints by means of a fiber-optic reflectance densitometric probe coupled to the movable cursor of a digitizing tablet. The cursor, with its attached probe, is moved by hand along a scan trajectory determined by the operator. In its configuration for use with 2-deoxyglucose autoradiographs, the histological section from which the autoradiograph was derived provides architectonic landmarks for guiding the path of the scan. The X, Y and density values taken along a scan line are sequentially stored in the computer memory. Algorithms are presented for plotting densities along unfolded scan lines within layers of structures with complicated shapes, for normalizing non-linearities introduced during photographic processing, for standardizing the data sets with reference to the density of average gray matter in different animals, for calculating total integrated density within defined boundaries along the scan line, for generating averages of multiple scans, and for stacking sequential scans to form pseudo-3-dimensional plots. This system allows densitometric measures to be made from autoradiographs in anatomically defined regions, thereby permitting precise correlation between isotope concentration and histological structure.

The central auditory pathway of the gerbil Psammomys obesus: a deoxyglucose study

The tonotopic organization of the central auditory pathway of the gerbil Psammomys obesus was mapped with deoxyglucose autoradiography under anesthesia. Animals, injected with tritiated deoxyglucose, were stimulated with 0.8, 2.5 and 17.0 kHz tone bursts monaurally in the free field and compared with non-stimulated controls. Apart from the medial geniculate body, all auditory structures showed sound-specific uptake of tracer. Frequency selective tracer accumulation could not be discriminated in the auditory cortex, the nuclei of the lateral lemniscus or the superior olivary complex. Isofrequency laminae could be determined most precisely in the dorsal cochlear nucleus and the central nucleus of the inferior colliculus. About half the mass of each of these nuclei is devoted to the processing of sound below 2.5 kHz. This disproportionately large representation of low frequencies matches the very high sensitivity of the peripheral auditory system in that range.

Effect of hyperbaric oxygen on 2-deoxy-D-glucose and L-glutamate transport in rat cortical synaptosomes

Initial velocities of uptake of L-glutamic acid and 2-deoxy-D-glucose (2-Dg) have been measured in cortical synaptosomes from rats which had been exposed to oxygen at high pressure (OHP) and compared to similar measurements in normobaric controls. Exposure to OHP had no significant effect on glutamate uptake at any combination of sodium and glutamate used. In contrast, OHP reduced 2-Dg uptake by an average of 17.5%. Although Kt was little affected, OHP exposure reduced apparent maximal transport capacity by 15%. Since hyperbaria with normal pO2 had no significant effect on uptake, the effect of OHP is an oxygen effect, rather than a pressure effect. The effects of OHP on uptake do not parallel the effects of age; glutamate transport capacity was reduced in aged animals, while 2-Dg transport was unaffected.

[Comparative distribution study of 14C labeled amino acids, glucose-analogue and precursor of nuclei acid, as tumor seeking agents]

As tumor-seeking agents, glucose analogues, natural amino acids, synthetic nonmetabolized amino acids, and precursor of nucleic acids, etc., labeled with positron emitter, such as 11C and 18F have been recently investigated. However, there are very few reports concerning comparative study of tumor uptake and tissue distribution of these agents. This preliminary paper describes comparative distribution and whole-body autoradiography of these agents. 14C labeled deoxy-2-fluoro-D-glucose (FDG), L-, DL-leucine, 1-aminocyclopentane carboxylic acid (ACPC), alpha-amino isobutyric acid (alpha-AIB), and thymidine were intravenously injected through tail vein into separate groups of the experimental animals. As the experimental animals, the mice with Ehrlich tumor and the rats with Hepatoma AH109A were used. Within 30 min after injection, FDG had the highest tumor uptake and tumor to tissue ratios, although FDG was inferior to ACPC and thymidine in related to tumor to heart, lung and brain ratios. However, the time course study indicated that tumor uptake of ACPC, alpha-AIB and D-leucine increased with time, whereas those of other agents decreased with time or reached a plateau. Thus, at 120 min after injection, ACPC had the highest tumor uptake and tumor to tissue ratios, although ACPC was inferior to FDG in related to tumor to blood, liver and pancreas ratios. Autoradiogram of ACPC showed very clear tumor image as well as that of FDG. The above data suggest that synthetic nonmetabolized amino acids, such as ACPC may be promising as tumor-seeking agents, when used with a single photon emission computed tomography, while glucose analogue such as FDG, are the best tumor-seeking agent, when used with a positron emission computed tomography.