Fructose is the most uptaken sugar for (-)-carvone biosynthesis in Mentha spicata L.

Mentha spicata L. cuttings were fedin vivo with ¹⁴C-palmitate, ¹⁴C-acetate, ¹⁴C-sucrose, ¹⁴C-glucose, and ¹⁴C-fructose. No labelled (-)-carvone was detected when cuttings were fed with ¹⁴C-palmitate and/or ¹⁴C-acetate, whereas feeding of cuttings with ¹⁴C-sucrose, ¹⁴C-glucose, and ¹⁴C-fructose resulted in labelled (-)-carvone biosynthesis. Among sugars, fructose feeding caused the highest (-)-carvone biosynthesis. The lack of incorporation of exogenous ¹⁴C-palmitate and/or ¹⁴C-acetate into (-)-carvone and the incorporation of sugars into this monoterpene, also confirm for this species the presence of an alternative, non-mevalonate biosynthetic pathway for monoterpene production.     

The effects of ovarian hormones on glucose and fatty acid oxidation during exercise in female ovariectomized rats

The effects of ovarian hormones on glucose and fatty acid oxidation during exercise were investigated in adult female ovariectomized rats. Rats subdivided into 3 groups received intraperitoneal injections of hormones or sesame oil for 8 days. Estrogen (E) treated rats received 17-beta estradiol in daily doses of 2 micrograms. Estrogen and progesterone treated rats (EP) received 17-beta estradiol in daily doses of 2 micrograms and 2 mg, respectively. Control rats (S) received sesame oil alone. After an overnight fast, rats ran at the speed of 25 m.min-1 for 60 min. [U-14C]glucose or [1-14C]palmitate was injected into rats at 5 min of exercise and before 10 min of exercise, respectively. Expired 14CO2 was collected using bottomless chamber on a treadmill belt. No significant differences were found in mean blood glucose, lactate and plasma free fatty acid concentrations after the exercise. Until the end of the exercise 34.7 +/- 2.6 (E, n = 5), 40.8 +/- 2.9 (EP, n = 5) and 43.7 +/- 3.5% (S, n = 6) (mean +/- SE) of 14C which was injected as 14C-glucose was recovered as 14CO2. During 60 min of the exercise 27.5 +/- 1.0 (E, n = 7), 19.8 +/- 2.7 (EP, n = 6) and 25.0 +/- 1.9% (S, n = 6) of 14C which was injected as 14C-palmitate was recovered as 14CO2. A significant difference was found in this rate between E and EP (P less than 0.05). It was concluded that estrogen treatment stimulated fatty acid oxidation compared with the estrogen plus progesterone treatment and tended to inhibit glucose oxidation during prolonged exercise.     

STUDIES OF MEMBRANE FORMATION IN TETRAHYMENA PYRIFORMIS : III. Lipid Incorporation into Various Cellular Membranes of Logarithmic Phase Cultures

When 1-¹⁴C-palmitic acid is used to pulse label logarithmic cultures of Tetrahymena pyriformis, radioactivity appears in lipids of the various membrane types at vastly differing rates. The microsomes and postmicrosomal supernatant attain a high specific radioactivity within 1 min, while the membranes enveloping the cilia require several hours to reach the microsomal level. A similar pattern is obtained when the tracer is sodium 1-¹⁴C-acetate or 8,9-³H-hexadecyl glycerol. In all fractions the phosphonolipid incorporates radioactivity from ¹⁴C-palmitate much less rapidly than do the other major phospholipids. The patterns of labeling suggest that new lipids are transported from a cytoplasmic site of synthesis to points of membrane fabrication throughout the cell.     

Determination of the reversible uptake of 3H-serotonin in synaptosomes: an adequate evaluation of the contribution of nonspecific uptake

Serotonin (5-HT) uptake in synaptosomes was studied at 0 degree C (1), at 37 degrees C in the presence of 100 microM imipramine (IIa) or 100 microM zimelidine (IIb), in the absence of Na+ ions (III) in the incubation medium. A significant decrease (P less than 0.01) of the uptake rate has been found (III greater than IIa, b greater than I). Nonspecific uptake inhibition was thought to be the cause of these differences. Determination of specific uptake, using control III, has shown Na+-dependent transport of 5-HT only on the one type of carrier (Km = 174 + 24 nM). It is concluded that determination of 5-HT nonspecific uptake, using control III, has permitted a more exact evaluation of specific uptake parameters, than determination, using controls I and IIa, b.     

Aldosterone induction of electrogenic sodium transport in the apical membrane vesicles of rat distal colon

Na-H exchange is present in apical membrane vesicles (AMV) isolated from distal colon of normal rats. Because in intact tissue aldosterone both induces amiloride-sensitive electrogenic sodium transport and inhibits electroneutral sodium absorption, these studies with AMV were designed to establish the effect of aldosterone on sodium transport. An outward-directed proton gradient stimulated 22Na uptake in AMV isolated from distal colon of normal and dietary sodium depleted (with elevated aldosterone levels) experimental rats. Unlike normal AMV, proton gradient-dependent 22Na uptake in experimental AMV was inhibited when uptake was measured under voltage-clamped conditions. 10 microM amiloride inhibited the initial rate of proton gradient-dependent 22Na uptake in AMV of normal and experimental rats by 30 and 75%, respectively. In contrast, 1 mM amiloride produced comparable inhibition (90 and 80%) of 22Na uptake in normal and experimental AMV. Intravesicular-negative potential stimulated 22Na uptake in experimental but not in normal AMV. This increase was inhibited by 90% by 10 microM amiloride. An analogue of amiloride, 5-(N-ethylisopropyl) amiloride (1 microM), a potent inhibitor of electroneutral Na-H exchange in AMV of normal rat distal colon, did not alter potassium diffusion potential-dependent 22Na uptake. Increasing sodium concentration saturated proton gradient-dependent 22Na uptake in normal AMV. However, in experimental AMV, 22Na uptake stimulated by both proton gradient and potassium diffusion potential did not saturate as a function of increasing sodium concentration. We conclude from these results that an electrically sensitive conductive channel, not electroneutral Na-H exchange, mediates 22Na uptake in AMV isolated from the distal colon of aldosterone rats.     

Characterization of Xylamine Binding to Proteins of PC12 Pheochromocytoma Cells

PC12 pheochromocytoma cells take up 3,4-dihydroxyphenylethylamine (dopamine) and norepinephrine by a Na+-dependent, cocaine-sensitive system. The kinetics suggest that the same transporter functions for both substrates. Xylamine, a nitrogen mustard that blocks catecholamine uptake into neurons, irreversibly inhibited norepinephrine uptake into PC12 (IC50 = 15 microM). Pretreatment with 10 microM xylamine did not inhibit norepinephrine transport if 10 microM cocaine or 100 microM norepinephrine was also present during the pretreatment period or if Na+ was absent. These results indicate that xylamine must interact with the norepinephrine transporter to inhibit norepinephrine uptake. PC12 accumulated [3H]xylamine; this uptake had Na+-dependent and Na+-independent components. The Na+-dependent uptake was saturable (Km = 13 microM), and it was inhibited by cocaine (IC50 = 0.6 microM), desipramine (IC50 less than 1 nM), and norepinephrine (IC50 = 1 microM). Several proteins became prominently labeled when intact PC12 cells were incubated with [3H]xylamine; these proteins were enriched in a plasma membrane fraction and have molecular weights of 17,000, 24,000, 31,000, 33,000, 41,000, 42,000, 52,000, and 80,000. Other proteins were labeled less prominently. The labeling of all proteins was markedly decreased when the incubation with [3H]xylamine occurred in the presence of cocaine, desipramine, gramicidin D, or in a Na+-free buffer. These results indicate that xylamine must be transported into the cells for covalent binding to proteins to occur. [3H]Xylamine labeled essentially the same proteins when incubated with cell homogenates, but competition experiments with bretylium, desipramine, and cocaine failed to reveal which of the [3H]xylamine-labeled proteins is associated with the norepinephrine transporter.     

Substance P enhances cation permeability of neuronal cell lines

Substance P stimulated the uptake of guanidinium in neuroblastoma X glioma hybrid cells and neuroblastoma cells but not in polyploid glioma cells. Guanidinium has previously been shown to pass the action potential Na+ channel in the two neuronal cell lines. Half-maximal stimulation was reached at 3 microM substance P and, with the hybrid cells, a saturation was seen above 10 microM. The analogue (D-Pro2,D-Trp7,9)-substance P, recently described as a substance P antagonist, caused a stimulation of guanidinium uptake comparable to that seen in the presence of substance P and did not inhibit the stimulation exerted by substance P. The pharmacological properties of the substance P-activated ion channel were investigated. Tubocurarine, phentolamine and propranolol blocked the substance P-stimulated guanidinium uptake with half-maximal inhibitory concentrations of 0.5, 5 and 50 microM. A similar characteristics has been found previously with the veratridine-activated Na+ channel in the cell lines investigated here. Peptides structurally related to substance P such as physalaemin and eledoisin, or others such as neurotensin, bradykinin, D-Ala2, Met5-enkephalinamide and ACTH(1-24) did not affect guanidinium uptake. In view of the high concentrations of substance P required for eliciting an effect in the cell lines, the involvement of specific receptors is questioned. A direct interaction of the peptide with the action potential Na+ channel is discussed.     

A bicarbonate-dependent process inhibitable by disulfonic stilbenes and a Na+/H+ exchange mediate 22Na+ uptake into cultured bovine corneal endothelium

22Na+ uptake into confluent monolayers of cultured bovine corneal endothelial cells was studied in the presence of ouabain (10(-4)M) to inhibit active sodium extrusion. In bicarbonate saline, uptake was reduced to a similar degree either by amiloride (10(-3)M) or by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (10(-3)M). A further reduction was obtained with SITS-pretreated cells in the presence of amiloride. SITS-sensitive uptake was further characterized in saline containing both ouabain (10(-4)M) and amiloride (10(-3)M). It was absolutely dependent on bicarbonate, which could not be substituted by other plasma membrane permeable buffers (50 mM acetate or 25 mM glycodiazine). It was a saturable function of both bicarbonate and sodium concentration. Half-maximal fluxes occurred between 3 and 7 mM HCO3 (at 151 mM Na) and between 35 and 60 mM Na (at 28 mM HCO3). Uptake into sodium-depleted cells was reduced as opposed to sodium-rich cells, and SITS-sensitive 22Na+ efflux out of 22Na+-loaded cells into sodium-free medium was less than efflux into sodium saline, indicating trans-stimulation by sodium. The amiloride-sensitive pathway was studied in the absence of bicarbonate to inhibit uptake via the SITS-sensitive pathway. 22Na+ uptake into sodium-depleted cells increased steeply with extracellular pH in the range between pH 6 and 8 and could be largely blocked by 10(-3), but not by 10(-5) M amiloride. It is concluded that bovine corneal endothelial cells possess at least two distinct pathways for sodium uptake, amiloride sensitive 22Na+ fluxes being mediated by a Na+/H+ antiport, while the SITS-sensitive process is probably identical to a bicarbonate-sodium cotransport system postulated earlier from electrophysiological studies.     

Carbohydrate transport in Moniliformis dubius (Acanthocephala). I. The kinetics and specificity of hexose absorption.

The uptakes of 14C-glucose, -2-deoxyglucose, -mannose, -N-acetylglucosamine, -3-0-methylglucose, -fructose, and -galactose by female Moniliformis dubius were nonlinear, saturable functions of hexose concentration. Kinetic and inhibition studies indicated that glucose and 2-deoxyglucose were absorbed via a single common transport locus. Mannose, N-acetylglucosamine, 3-0-methylglucose, fructose, and galactose (in decreasing order of effectiveness) inhibited the uptake of glucose in a completely competitive manner; their absorptions appeared to be mediated by the glucose transport locus and, to some degree, by one or more additional transport systems. Kinetic studies suggested that the apparent inhibitions of 14C-glucose uptake by maltose and glucose-6-phosphate were due to free glucose liberated through the action of surface hydrolases. The uptake of 14C-glucose was also inhibited by salicin, alpha-methylglucoside, and beta-methylglucoside, but not by pentoses, L-hexoses, sugar alcohols, disaccharides (except maltose), gluconic acid, glucuronic acid, phlorizin, or ouabain. Glucose uptake was not Na+-dependent.     

Indomethacin inhibits the uptake of 22sodium by ovine trophoblastic tissue in vitro

Blastocysts from several species synthesize prostaglandins in vitro, but the exact functions of the prostaglandins are unknown. The purpose of this study was to determine if indomethacin, an inhibitor of prostaglandin synthesis, would inhibit the uptake of 22sodium ([22Na]) by ovine trophoblastic tissue. To determine the concentration of indomethacin that would inhibit the synthesis of PGF2 alpha and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) by blastocysts, blastocysts were collected from ewes 16 days after mating, sliced into pieces approximately 2 mm in length and incubated for 48 h at 37 degrees C in 2 ml of medium containing either 0, 0.2, 0.4, 0.8 or 1.6 mM of indomethacin. Concentrations of indomethacin greater than or equal to 0.2 mM reduced (P less than .01) trophoblastic release (ng/micrograms DNA) of PGF2 alpha from 205 +/- 71.2 to less than or equal to 3.3 +/- 0.2, reduced PGFM from 0.7 +/- 0.1 to less than or equal to 0.17 +/- 0.01, and inhibited formation of trophoblastic vesicles. In a second experiment, blastocysts were recovered from ewes 16 days after mating and pieces of trophoblast were incubated with [22Na] and either 0 or 0.4 mM of indomethacin. Indomethacin reduced the uptake of [22Na], which is an indirect measure of the transport of water across epithelia, from 3680 +/- 1118 to 934 +/- 248 cpm/micrograms DNA (P less than .03) and prevented formation of trophoblastic vesicles. Prostaglandins produced by ovine blastocysts might be involved in controlling uptake of water, which is essential for expansion of blastocysts.     

Uptake of U-14C-glucose by Streptococcus mutans in the presence of saccharin

The uptake of U-14C-glucose by resting cells of Streptococcus mutans OMZ-176 was studied in the presence of the artificial sweetener saccharin as well as sodium chloride. Glucose grown cells were resuspended in phosphate buffer (0.05 M, pH 7.8), and the uptake of U-14C-glucose was observed for 150 min in time intervals of 30 min, in the presence of 0.02 and 2.00 mg/ml of sodium saccharin as well as sodium chloride. As compared to the control and the sodium chloride treatments, sodium saccharin at the highest concentration range more than doubled the accumulation of radioactive labelled carbon within the cells.     

Increased Na(+)-dependent D-glucose transport and altered lipid composition in renal cortical brush-border membrane vesicles from bile duct-ligated rats.

Erythrocyte membranes of patients with liver disease are characteristically enriched in cholesterol, a change known to impair several carrier-mediated membrane transport functions. In the present study we have assessed whether experimental liver disease can affect the membrane lipid composition and transport function of kidney epithelial cells. Small (about 5%) but significant (P less than 0.01) increases were found in the cholesterol-to-phospholipid molar ratio (C/PL) of rat renal cortical brush-border membrane (BBM) vesicles 3, 8, and 15 days after bile duct ligation which correlated closely with increased fluorescence polarization, i.e., decreased membrane fluidity (r = 0.75, P less than 0.001; n = 27). A lipoprotein-mediated pathogenesis was suggested by the close relationship between BBM C/PL and plasma C/PL (r = 0.69, P less than 0.001). The mean high-affinity Na(+)-coupled D-glucose uptake by BBM vesicles was higher 1, 3, 8, and 15 days after ligation than in non-operated rats, significantly so at 3 and 8 days (611 +/- 37 and 593 +/- 22 vs. 507 +/- 21 pmol/mg protein per 4 sec; P less than 0.05), and was positively correlated with BBM C/PL (r = 0.58, P less than 0.01) and fluorescence polarization (r = 0.41, P less than 0.05). Brief incubation of BBM vesicles from normal rats with cholesterol-rich phospholipid liposomes simultaneously increased BBM C/PL and Na(+)-dependent D-glucose uptake. Stimulation of BBM Na(+)-glucose cotransport in ligated rats was not due to delayed dissipation of the Na+ gradient or to a more rapid development of membrane potential. High-affinity Na(+)-dependent D-glucose uptake kinetics in 3-day bile duct-ligated rats showed a lower Kt, without an alteration in maximum velocity, Vmax, compared to sham-operated animals (0.298 +/- 0.015 vs. 0.382 +/- 0.029 mM; P less than 0.05), whilst the binding dissociation constant, Kd of high-affinity phlorizin binding sites was reduced by ligation (0.453 +/- 0.013 vs. 0.560 +/- 0.015 microM; P less than 0.001). We conclude that an early effect of bile duct ligation is to enrich renal cortical brush-border membranes in cholesterol, thereby decreasing membrane fluidity and stimulating Na(+)-dependent D-glucose uptake by increasing the affinity of the carrier.     

(Na,K)-ATPase-mediated cation pumping in cultured rat hepatocytes. Rapid modulation by alanine and taurocholate transport and characterization of its relationship to intracellular sodium concentration

(Na,K)-ATPase is thought to maintain the transmembrane electrochemical sodium gradient which powers secondary active sodium-coupled transport of a variety of solutes including amino acids and bile acids. However, little is known regarding the effect of sodium-coupled solute transport on intracellular sodium concentration ( [Na]ic) and on (Na,K)-ATPase-mediated cation pumping in the intact cell. In order to address this question, we have measured 22Na uptake rate, steady state 22Na content, and ouabain-suppressible 86Rb uptake rate in primary cultures of adult rat hepatocytes under a variety of conditions. Compared with control conditions (sodium uptake rate = 6.00 +/- 0.40 nmol X min-1 X mg-1; [Na]ic = 11.96 +/- 0.54 mM; cation pumping = 2.53 +/- 0.18 nmol X min-1 X mg-1), cation pumping was increased by taurocholate (less than or equal to 158%), alanine (less than or equal to 246%), monensin (less than or equal to 400%), and cold exposure (less than or equal to 525%), and this increase was accompanied by increases in Na uptake and [Na]ic. In contrast, preincubation in low sodium medium decreased all three variables. These changes in cation pumping were blocked in the absence of extracellular sodium and were not accompanied by changes in ouabain-suppressible ATP hydrolysis measured in cell homogenate. An overall plot of cation pumping versus [Na]ic yielded a sigmoid-shaped curve. Values for KNa (17.8 +/- 1.4 mM) and Vmax (8.98 +/- 0.62 nmol X min-1 X mg-1) for cation pumping were estimated assuming three sodium sites per pump unit. These findings indicate that: 1) uptake of alanine and taurocholate is associated with a rapid increase in (Na,K)-ATPase cation pumping; 2) this increase probably results from an increase in pumping per pump unit rather than an increase in the total number of pump units, and it appears to be mediated via an increase in sodium influx and [Na]ic; 3) [Na]ic under control conditions is close to the apparent KNa of cation pumping, implying that substrate availability may be the mechanism whereby sodium uptake is tightly linked to (Na,K)-ATPase cation pumping in intact hepatocytes.     

Regulation and rate of the hexose monophosphate shunt in Rana ridibunda erythrocytes

1. Resting rates of Rana ridibunda erythrocyte glucose consumption and 14CO2 production from 1-14C-glucose were found to be significantly lower than the respective values in human erythrocytes. 2. In the presence of 1-14C-glucose Methylene Blue stimulated 14CO2 production 7-fold, while in the presence of 6-14C-glucose Methylene Blue stimulated 14CO2 production 1.2-fold. 3. The Km of G-6-PD for G-6-P and NADP were 29 and 12 microM, respectively while the Km of 6-PGD for 6-PG and NADP were 83 and 32 microM, respectively. The Ki of G-6-PD and 6-PGD for NADPH were 80 and 12 microM, respectively. 4. Excess amounts of NADP resulted in a significant decrease of 14CO2 production from 1-14C-glucose in total haemolysates. 5. ATP, ADP and fructose diphosphate inhibited both G-6-PD and 6-PGD, the latter being more sensitive than G-6-PD to their inhibitory effect, 2,3-DPG and reduced and oxidized glutathione showed a marked inhibitory effect on 6-PGD, while the phosphorylated trioses inhibited only G-6-PD. 6. Physiological concentrations of oxidized glutathione decreased the inhibition exercised by NADPH on G-6-PD. 7. The possible role of the two dehydrogenases in the regulation of the HMS is discussed.     

Induction of a sodium ion influx by progesterone in human spermatozoa

In human spermatozoa, progesterone (P(4)) induces a depolarization of the plasma membrane, a rapid calcium (Ca(2+)) influx, and a chloride efflux. The sodium ion (Na(+)) was partly responsible for the P(4)-induced depolarizing effect but was not required for calcium influx. We used fluorescent probes for spectrofluorometry to investigate whether P(4) induced a Na(+) influx and whether voltage-operated channels were involved in Na(+) and/or Ca(2+) entries. We found that 10 microM P(4) significantly increased intracellular Na(+) concentration from 17.8 +/- 2.0 mM to 27.2 +/- 1. 6 mM (P < 0.001). Prior incubation of spermatozoa with 10 microM flunarizine, a Na(+) and Ca(2+) voltage-dependent channel blocker, inhibited the sodium influx induced by 10 microM P(4) by 84.6 +/- 15.4%. The Ca(2+) influx induced by 10 microM P(4) was also significantly inhibited in a Na(+)-containing medium by 10 microM flunarizine or 10 microM pimozide (P < 0.01). In contrast, flunarizine had no inhibitory effect on the Ca(2+) influx induced by 10 microM P(4) in spermatozoa incubated in Na(+)-depleted medium. The P(4)-promoted acrosome reaction (AR) was significantly higher when spermatozoa were incubated in Na(+)-containing medium as compared to Na(+)-depleted medium. These data demonstrate that P(4) stimulates a Na(+) influx that could be involved in the AR completion. They also suggest that voltage-dependent Na(+) and Ca(2+) channels are implicated in P(4)-mediated signaling pathway in human spermatozoa.     

Cyclic nucleotide metabolism in the human erythrocyte

Erythrocytes, which show little or no guanylate or adenylate cyclase activity, take up cyclic nucleotides from blood. Studies were done by incubating human erythrocytes in isotonic medium with the dibutyryl derivatives of cAMP and cGMP and in a hypotonic medium in which the cells are partially hemolyzed and, therefore, freely permeable to cAMP and cGMP. At cAMP and cGMP concentrations of 50 microM and above, the amount of 14CO2 generated from 1-14C-glucose was decreased significantly. This effect was suppressed by 4.6 mM theophylline. Inosine and ribose, which are catabolites of cAMP and cGMP also decreased formation of 14CO2 from 1-14C-glucose. Accordingly, it is postulated that in the absence of theophylline, the activity of phosphodiesterase resulted in AMP and GMP formation. These mononucleotides enter into the purine salvage pathways to form ribose phosphate. Additionally, the production of lactate and 2,3-diphosphoglycerate (2,3-DPG) was measured in human erythrocytes after incubation with the dibutyryl derivatives of cAMP (bt2-cAMP) and cGMP (bt2-cGMP). At a concentration of 0.1 microM, bta2-cGMP inhibits lactate production at 60 min (p less than 0.01). Slight increases in 2,3-DPG were not statistically significant. Catabolism of cyclic nucleotides may prevent diffusion equilibria allowing for the erythrocyte's continuous uptake of cyclic nucleotides and providing a detoxification mechanism that could compensate for conditions in which elevations of these substances are observed.     

Energetics of alanine, lysine, and proline transport in cytoplasmic membranes of the polyphosphate-accumulating Acinetobacter johnsonii strain 210A.

Amino acid transport in right-side-out membrane vesicles of Acinetobacter johnsonii 210A was studied. L-Alanine, L-lysine, and L-proline were actively transported when a proton motive force of -76 mV was generated by the oxidation of glucose via the membrane-bound glucose dehydrogenase. Kinetic analysis of amino acid uptake at concentrations of up to 80 microM revealed the presence of a single transport system for each of these amino acids with a Kt of less than 4 microM. The mode of energy coupling to solute uptake was analyzed by imposition of artificial ion diffusion gradients. The uptake of alanine and lysine was driven by a membrane potential and a transmembrane pH gradient. In contrast, the uptake of proline was driven by a membrane potential and a transmembrane chemical gradient of sodium ions. The mechanistic stoichiometry for the solute and the coupling ion was close to unity for all three amino acids. The Na+ dependence of the proline carrier was studied in greater detail. Membrane potential-driven uptake of proline was stimulated by Na+, with a half-maximal Na+ concentration of 26 microM. At Na+ concentrations above 250 microM, proline uptake was strongly inhibited. Generation of a sodium motive force and maintenance of a low internal Na+ concentration are most likely mediated by a sodium/proton antiporter, the presence of which was suggested by the Na(+)-dependent alkalinization of the intravesicular pH in inside-out membrane vesicles. The results show that both H+ and Na+ can function as coupling ions in amino acid transport in Acinetobacter spp.     

Characterization of glucose uptake by Trichuris globulosa (Nematoda) in vitro

14C-glucose uptake by adult Trichuris globulosa is found to be a non-linear function of time and limiting substrate concentration. The uptake is a two component process, an initial rapid burst is followed by a lower steady state, implying a mediated process. The uptake is dependent on Na+ ions which cannot be replaced by K+, Li+ or choline. The uptake is also dependent on pH, being maximal at pH 7.4. 14C-glucose absorption is markedly inhibited by glucose, phlorizin, ouabain and to a smaller extent by a number of monosaccharides and other sugar-phosphates, nucleosides and metabolic inhibitors like p-nitrophenyl phosphate and iodoacetate. The inhibition constant for glucose, phlorizin and ouabain has been found to be 8 mM, 5 mM and 7 mM, respectively. A modified Dixon-plot shows that glucose is a completely competitive inhibitor for 14C-glucose uptake while the nature of competitive inhibition of phlorizin and ouabain are found to be partial.     

Na(+)-dependent high-affinity uptake of L-glutamate in cultured fibroblasts.

Uptake of 1 microM [3H]L-glutamate by cultured 3T3 fibroblasts was strongly dependent on extracellular Na+; it was reduced by elevated concentrations of K+ (60 mM) but it was not influenced by variations in the concentration of Ca2+ (0-9.6 mM). D- and L-Asparate, D- and L-threo-3-hydroxyaspartate DL-threo-3-methylaspartate and a few other glutamate derivatives and analogues inhibited the uptake but several close analogues of L-glutamate (including D-glutamate) had no effect, implying that the uptake system is highly structurally selective. The recently identified inhibitor of glutamate uptake in synaptosomal preparations, L-trans-pyrrolidine-2,4-dicarboxylate, was also among the inhibitors. Apparent Km of the uptake was found to be less than 10 microM. The present observations indicate that Na(+)-dependent 'high-affinity' uptake of L-glutamate may appear in structures which are apparently unrelated to glutamatergic synaptic transmission in the CNS.     

Effects of low water potentials on some aspects of carbohydrate metabolism in Chlorella pyrenoidosa

Summary Chlorella pyrenoidosa was subjected to low water potentials and the resulting changes in carbohydrate metabolism were measured.Water deficit reduced the incorporation of ¹⁴C-glucose into methanol insoluble compounds, principally starch and increased that into sucrose. Even moderate water deficit, for example potentials of -2.5 and -5 atm, greatly reduced the incorporation of ¹⁴C-glucose into uridine diphosphate glucose, while ¹⁴C levels of the hexose monophosphates changed little, indicating a direct stimulus of sucrose synthesis. This increased sucrose synthesis was one of the earliest effect of water deficit, because potentials of -2.5 and -5 atm did not reduce respiration and glucose uptake.At lower water potentials (-10 atm or less) there was reduced ¹⁴C incorporation into all sugar phosphates. This resulted from a combination of reduced ¹⁴C-glucose uptake and increased sucrose synthesis.Water potentials as low as -20 atm had little effect on acetate uptake, or on the ¹⁴C levels in the intermediates of the TCA cycle. This confirmed that low water potentials do not directly inhibit respiratory pathways in Chlorella.The results are discussed in relation to the effect of water deficit on levels of various metabolites in vascular plants, which have been reported by other workers.