Neutral amino acid transport systems of tissue culture cells

We have studied the interactions among a varied group of neutral amino acids for uptake into two different animal tissue culture cell lines. 3T3 mouse cells and Chinese hamster ovary cells were used in these studies. The results showed that the affinities of the amino acids clustered into two groups, one including amino acids such as glycine, alanine, and alpha-aminoisobutyric acid and the other group included amino acids such as leucine and phenylalanine. The specificities and properties of these systems are similar to those described earlier for the Ehrlich ascites cell, System A (alanine-preferring) and System L (leucine-preferring). System A is highly concentrative, sensitive to sodium ion, and serves only poorly for exchange while System L is not very concentrative or sensitive to alkali metal ion, although it serves very well for exchange with endogenous amino acids. The kinetic parameters for several amino acids are reported and other properties of the transport systems are discussed.

Regulation of amino acid transport activity and growth rate of animal cells in culture

Balb/3T3 mouse cells grown in cell culture contain the A and L systems for neutral amino acid transport. L-Alanine was used as a test amino acid for the A system and L-leucine for the L system. Transport activities for both transport systems are altered as the growth conditions for the cells are altered. When cell growth was arrested by allowing cells to approach confluency, or by the removal of serum or by the addition of protein synthesis inhibitors, System A transport activity decreased and System L activity increased significantly. The content of the cellular amino acids increased 2- to 3-fold whenever cell growth was arrested by the conditions stated above. Increased cellular amino acids, therefore, are associated with decreased transport activity of System A and increased activity of System L. Altering cellular amino acids by loading or depleting the cells produced the predicted responses for the rapidly exchanging L-system but System A was less responsive. It is possible that regulatory mechanisms operate for the A system other than the direct action of alterations in cellular amino acid levels. The implications of the amino acid transport activity changes observed here on various studies on the role of transport in cell growth regulation and malignant transformation are discussed.

An eye screening program in a Chinese-Canadian community

A screening program staffed by ophthalmologists, ophthalmology residents, ophthalmic assistants, social workers and Chinese-speaking volunteers and directed at a Chinese immigrant community, was conducted at the Mount Sinai Hospital, Toronto. The Chinese population had been hesitant to use our hospital facilities and we hoped to overcome their fears, as well as to detect previously undiagnosed ocular problems. The program succeeded in finding many eye problems, some serious, and in encouraging this immigrant group to come for proper medical care. We describe the method of setting up and conducting such an undertaking, which involved the Departments of Ophthalmology and Social work, hospital administrators and volunteers from the community.

Evidence for carrier-mediated transport of melphalan by L5178Y lymphoblasts in vitro

Mechanism of transport of the alkylating agent [14C]melphalan was investigated in L5178Y lymphoblasts in vitro. A time course of melphalan uptake was approximately linear for 5 to 10 min and thereafter entered a plateau region. Evidence that unidirectional influx of melphalan is carrier mediated was that uptake obeyed simple Michaelis-Menten kinetics, that it demonstrated chemical specificity, and that the cell/medium distribution ratio of drug decreased with increasing extracellular drug concentration. The kinetic parameters for melphalan transport consisted of a Km (mean +/- S.E.) of 1.53 +/- 0.18 X 10(-4) M and a transport capacity (Vmax) of 3.48 +/- 0.31 X 10(-17) mole/min/cell. Findings suggesting that transport was at least in part energy dependent and not simply a passive process were that drug uptake was temperature sensitive and sodium dependent. Analysis of cell sap constituents indicated the presence of intact drug within the cell. The percentage of radioactivity (mean +/- S.D.) found in the cell sap fraction was 95.8 +/- 2.2% of total cell activity, and 92.6 +/- 4.1% of this was trichloroacetic acid soluble. Thin-layer chromatography of the cell sap fraction and medium each revealed that the majority of radioactivity migrated as a single peak with an RF value identical with that obtained for free drug. The alkylating potential of intact drug complicated interpretation of the finding of apparent uphill transport against a concentration gradient. This observation, together with the relatively low cell-medium ratio (mean +/- S.D.) of 3.07 +/- 1.07, favors the concept that melphalan transport occurs by a facilitated diffusion process, although an active transport system has not been entirely excluded. The relative insensitivity of melphalan uptake to a wide range of metabolic inhibitors also suggests that transport is by a facilitated diffusion mechanism rather than an active process. Other alkylating agents and several amino acids including the L and D isomers of phenylalanine did not inhibit melphalan transport; thus a native substrate was not identified for the melphalan carrier and transport was by a mechanism separate from that of other alkylating agents.

Microtubules and pancreatic amylase release by mouse pancreas in vitro

The effects of vinblastine and colchicine on pancreatic acinar cells were studied by use of in vitro mouse pancreatic fragments. Vinblastine inhibited the release of amylase stimulated by bethanechol, caerulein, or ionophore A23187. Inhibition required preincubation with vinblastine,and maximum inhibition was observed after 90 min. Inhibition was relatively irreversible and could not be overcome by a high concentration of stimulant. Inhibition could also be produced by colchicine although longer preincubation was required and inhibition was only partial. Uptake of [3H]vinblastine and [3H]colchicine by pancreatic fragments was measured and found not to be responsible for the slow onset of inhibition by these drugs. In incubated pancreas, microtubules were present primarily in the apical pole of the cell and in association with the Golgi region. Vinblastine, under time and dose conditions that inhibited the release of stimulated amylase, also reduced the number of microtubules. The only other consistent structural effects of vinblastine were the presence of vinblastine-induced crystals and an increased incidence of autophagy. The remainder of cell structure was not affected nor were overall tissue ATP and electrolyte contents or the stimulant-induced increase in 45Ca++ efflux. It is concluded that the antisecretory effects of vinblastine and colchicine are consistent with a microtubular action, but that acinar cell microtubules are more resistant to the drugs than many other cell types.

Cigarette smoking and cancer of bladder and lung

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Oxygen-hemoglobin equilibrium of normal and glutathione-deficient sheep

The affinity of hemoglobin for oxygen did not differ significantly between normal and glutathione-deficient sheep. Although phlebotomy in sheep of both types did not significantly alter the partial pressure values at which hemoglobin is 50% saturated with oxygen, it did increase significantly the erythrocyte glutathione and 2,3-diphosphoglycerate (GSH) and (DPG) concentrations. Because DPG does not bind to sheep hemoglobin, its increase in hypoxic sheep must mean DPG is metabolically controlled in the absence of physiologic effect.

How phlebotomy affects the erythrocyte metabolism of high- and low-glutathione sheep

Erythrocyte glutathione concentration increases dramatically in low-glutathione sheep of the Finnish-Landrace breed. To determine if this phenomenon occurs in low-glutathione sheep of the Corriedale or Merino type, the packed cell volume was decreased to less than 16 by phlebotomy. Glutathione concentrations increased in high- and low-glutathione sheep. Low-glutathione sheep returned to pre-phlebotomy levels by the 18th day; high-glutathione sheep increased, then decreased below pre-phlebotomy levels for the duration of the experiment. Packed cell volumes increased linearly (1-07 per cent per day) for 19 days. The maximum reticulocyte percentage (11-4) occurred on the eight day. Some erythrocyte enzymes increased as the mean cell age decreased, but some did not change. Erythrocyte adenosine-5'-triphosphate and creatine appear to be related to the reticulocyte count.

Acquired sensory control of satiation in man

Lean male and female subjects who had been taking their meals as usual were given a 100 ml drink of starch immediately before a sandwich lunch. In the training phase,65 per cent starch was given before lunches which included a yoghurt-based dessert of one flavour and 5 per cent starch was given before another flavour. Subjects who initially ate lunches of similar size following the two drinks began after several pairings to take larger lunches following dilute starch than following concentrated starch. In extinction tests, identical 35 per cent starch drinks were given before lunches including desserts of either flavour. Lunches including the flavour hitherto paired with dilute starch remained larger than lunches including the other flavour, at least initially in extinction. Some of the difference in intake occurred in the dessert itself. None was attributable to differences in the early stage of the lunches. These results extend to man recent demonstrations that the satisfying power of a foodstuff is in part acquired by association of its sensory characteristics with some consequence of ingesting the nutrients which are consistently taken with or in that food. This consequence may be rapid intestinal absorption of glucose during or shortly after sensory input. The nature of the intake-suppressing response remains to be determined.

Vitamin E supplementation and glutathione peroxidase activity

Both excess dietary vitamin E and vitamin E deficiency in rats can significantly depress the activity of GSH peroxidase in liver and plasma of rats. Of all the six levels of vitamin E tested in this study, the dietary level of vitamin E found to maintain the maximum activity of GSH peroxidase in tissues of rats was somewhere between 25 and 250 IU/kg diet. This study conclusively indicates that the excess dietary vitamin E represses GSH peroxidase activity.

Estimating erythrocyte glyceraldehyde-3-phosphate dehydrogenase by a new method

A semi-quantitative fluorimetric assay for glyceraldehyde-3-phosphate dehydrogenase has been described. This method was applied to a number of animal species and correlates well with the standard spectrophotometric method.

Reactions of methyl radicals. I. Hydrogen abstraction from dimethyl sulphide

Hydrogen abstraction from (CH3),S and CH3COCH3 by CH3 radicals CH3+CH3SCH3 → CH4+CH3SCH2 CH3 + CH3COCH3 → CH4 + CH3COCH2 has been studied in the temperature range 120-245�. The rate constants, based on the value of 1013.34cm3 mol-l s-1 for the recombination of CH3 radicals, are given by (k in cm3 mol-1 s-1, E in kJ mol-1, R = 0.008314 kJ K-1 mol-1): logk1 = (11.62 � 0.08) ? (38.35 � 0.68)/2.303RT logk3 = (11.61 � 0.05) ? (40.48 � 0.46)/2.303RT Combination of the results for (1) with thermochemical data gives a calculated value of Logk-1 = (11.8 -63.7/2.303RT for the rate constant of the reverse reaction. The results for CH3+(CH3)2S are compared with all of the available data for hydrogen abstraction by free radicals from both sulphur-containing compounds, and molecules of the type (CH3)xM.

Transport of amino acids in intact 3T3 and SV3T3 cells. Binding activity for leucine in membrane preparations of ehrlich ascites tumor cells

Transport of amino acids into 3T3 and SV3T3 (SV40 virus-transformed 3T3) cells was measured on glass cover slips. The 3T3 and SV3T3 cells contain both A (alanine preferring) and L (leucine prefferring) systems for neutral amino acid transport. Initial rates of uptake of amino acids are about twofold higher in SV3T3 than in 3T3 cells. Other parameters measured, however, do not indicate marked differences in the transport of amino acids by the two cell types. L-system amino acids, such as leucine, are subject to trans-stimulation in both cell lines, whereas A-system amino acids, such as alanine and glycine, are not. Leucine was transported to higher levels in confluent cells than in nonconfluent cells. Glycine, however, shows distinctly less transport activity as the cells become confluent. Ehrlich ascites cell plasma membranes were prepared and assayed for amino acid-binding activity. Leucine-binding activity was detected by equilibrium dialysis in Triton X-100-treated membrane preparations.