Uptake of L-histidine, L-proline, L-tyrosine and L-ornithine by brain, intestinal mucosa, testis, kidney, spleen, liver, heart muscle, skeletal muscle and erythrocytes of the rat in vitro

Alpha-aminoisobutyric acid transport into human glia and glioma cells in culture

The AIB transport into human glia and glioma cells in culture has been studied. Because of the high affinity of AIB to the plastic culture dishes, a special washing technique had to be developed. With this technique, it was possible to perform transport experiments in a single plate containing about one million cells. The cells were viable, intact and adhered to the supporting medium throughout the experiment. The AIB transport into both types of cells was Na+-dependent and showed saturation kinetics when the small component of the transport due to diffusion had been subtracted. The AIB transport capacity of neoplastic glioma cells was 3.6 times higher than that of glia cells. This difference was related to the Vmax-values for the two types of cells. The apparent Km-values were the same. Inhibition experiments with other amino acids support the view that AIB is transported via System A in both glia and glioma cells. Sulfhydryl reagents (ethacrynic acid and NEM) and cytochalasin B clearly inhibited the AIB transport into glia cells whereas the effect on glioma cells was minimal.

Changes in amino acid influx with Na flow in incubated slices of mouse brain

The uptake of amino acids into slices of adult and newborn mouse brain was studied in relation to Na+ flow. (1) The level of Na+ and K+ incubated slices of brain depends on the ionic composition of the incubation medium. The intracellular levels of Na+ in adult tissue are below, in fetal tissue above, Na+ levels in the medium used. Rapid net flow into or out of the tissue can be achieved by transferring slices into media of higher or lower Na+ content. (2) Under conditions of net Na+ inflow, the influx of all amino acids tested increased; under conditions of net Na+ outflow, the influx of all amino acids decreased, as compared to slices in ionic equilibrium. The absolute levels of Na+ in the tissue under the experimental conditions had little effect on amino acid uptake. The stimulatory effect of Na+ inflow and the inhibitory effect of Na+ outflow could be observed at all developmental stages--in adult, newborn, and fetal tissue. (3) We conclude that ion movements influence metabolite transport; these effects are smaller in the absence of fully developed ion pumps. The direction of the net ion flow does not seem to be the main determinant: active accumulation occurred both in adult and in fetal brain, although the tissue-to-medium Na+ gradients were in opposite directions; in addition, amino acid inflow occurred in the presence of Na+ outflow.

Amino acid reabsorption in the rat nephron. Free flow micropuncture study

The concentration of nine endogenous free L-alpha-amino acids (ALA, LEU, ILE, PHE, TYR, LYS, GLU, PRO, GLY) and of taurine were determined simultaneously along the nephron of the rat kidney using free-flow micropuncture techniques without altering plasma amino acid concentration or kidney function. The amount of each amino acid was determined after dansylation (14C-labelled dansyl-chloride) in the micropuncture sample followed by thinlayer chromatography. The main site of reabsorption is the proximal tubule. After 15-20% of the proximal tubule length the bulk of reabsorption has taken place (18.9 plus or minus 3.4% S.E. of the filtered load remaining). Net reabsorption continues to a small but significant extent along the distal nephron (disal tubule and collecting duct). Reabsorption of taurine is less rapid (% remaining of filtered load at the early proximal tubule 37.0 plus or minus 4.6%). The transtubular concentration ratio of all amino acids except taurine follows a homogeneous course. Under the experimental conditions of this study no distction with respect to different systems of reabsorption "neutral", "basic", "acidic", "imino-glycine") could be made.

The uptake and incorporation of nucleosides into normal erythrocytes and erythrocytes containing Plasmodium berghei

Normal mouse erythrocytes and erythrocytes containingPlasmodium bergheiwere incubated for 1 h in a medium containing either adenosine, guanosine, cytidine or thymidine labelled with14C or3H. The purine nucleosides, adenosine and guanosine, but not the pyrimidine nucleosides, cytidine and thymidine, were incorporated into the nucleic acid of the parasite–host cell complex. The concentration achieved by all four nucleosides in both normal and parasitized cells was at least as high as that in the suspending medium, showing that not only purines but also pyrimidines enter the parasitized erythrocyte.

The movement of amino acids between blood and skeletal muscle in the rat

1. The rates of entry of twenty of the blood amino acids into skeletal muscle of living rats were measured directly by means of a technique which ensured that a steady concentration of a radioactively labelled amino acid is reached rapidly and is maintained in the bloodstream.2. The rates of entry were measured in experiments of short duration to avoid possible artifacts caused by amino acids leaving the muscle or by their metabolism.3. The entry rate of each amino acid increased in direct proportion to its concentration in the blood plasma over the physiological range.4. The various amino acids had widely different rates of entry. These rates could not be correlated with the physicochemical properties of the amino acids.5. Two amino acids, L-lysine and L-threonine, enter muscle against a concentration gradient, while in the case of a third, L-arginine, the blood concentration was raised high enough to induce saturation of the entry mechanism.6. It is concluded that entry takes place in vivo by means of carrier-mediated transport processes with a high degree of specificity.7. When the concentration of an amino acid in the bloodstream was increased to about twice normal the proportion of the additional amino acid that was taken up rapidly by the muscle was large enough, especially for the essential amino acids, to suggest that the tissue constitutes a quantitatively important storage system helping to regulate the concentrations of amino acids in the bloodstream.

The uptake and efflux of L-phenylalanine and L-tyrosine from rat brain cerebral cortex slices

The uptake of radioactive l-phenylalanine and l-tyrosine into the tissue water of rat brain cerebral cortex slices was shown to have saturation kinetics. The apparent K(m) for the uptake of l-phenylalanine was 0.86mm and for l-tyrosine was 1.64mm; for phenylalanine the apparent V(max.) value was 0.64mumol/min per ml of tissue water, and for l-tyrosine it was 0.98mumol/min per ml of tissue water. The accumulation of the two amino acids by the tissue was depressed in the absence of O(2), at 0 degrees C, or in the presence of metabolic inhibitors. The influxes and effluxes of both l-isomers were more rapid than those of the d-isomers. Competition between these two amino acids and each with l-tryptophan in respect of uptake into tissue water was shown. Their rates of influx were faster, and rates of efflux were slower, in the presence than in the absence of Na(+). It was concluded that these amino acids were taken up by active transport via a carrier mechanism.

Evidence against adrenergic motor transmission in the guinea-pig vas deferens

1. Field stimulation of desheathed preparations of guinea-pig vas deferens, treated with a ganglion-blocking agent, has revealed the presence of two tetrodotoxin-susceptible components in the motor response, suggesting the existence of two sets of post-ganglionic motor nerve fibres of different excitability: one set responding maximally to pulses of 0.1-0.4 msec; the other, to pulses of 2 msec. No distinction could be made pharmacologically between the two components.2. Cooling potentiated that component in the twitch-responses which was due to stimulation of the more excitable fibres.3. The sensitivity of the longitudinal muscle to the motor action of noradrenaline was low and was subject to considerable animal variation. But normal responses to post-ganglionic field stimulation were elicited in noradrenaline-insensitive preparations, in which the twitches elicited by 5 pulses could not be matched with noradrenaline, even 100-125 mug/ml.4. In some forty experiments, small doses of noradrenaline inhibited the twitch-responses evoked by either set of motor fibres. This inhibition differed from that produced by isoprenaline in two respects. Firstly, propranolol did not antagonize the noradrenaline inhibition, thus excluding an action on beta-adrenoceptors; and secondly, noradrenaline did not depress contractions elicited by muscarine or by 5-methylfurmethide.5. Phenoxybenzamine, 10(-6) g/ml., produced a thousandfold reduction in the sensitivity of the muscle to the motor action of noradrenaline, without any decrease in the height of the twitches elicited by 0.1 or 1 msec pulses.6. The twitch-responses were not affected by combined alpha + beta adrenoceptor blockade with phentolamine and propranolol.7. Tyramine, amphetamine, tranylcypromine and prostaglandin E(2) inhibited the twitches but potentiated the contractile effect of noradrenaline.8. The twitch-responses and their inhibition by noradrenaline were present in preparations taken from reserpinized animals.9. Although the twitch-responses could be paralysed by bretylium or guanethidine, the foregoing results excluded adrenergic transmission at the motor endings. Cholinergic transmission was also excluded by negative findings with anticholinesterases, atropine, nicotine and (+)-tubocurarine.10. Motor transmission by histamine, 5-hydroxytryptamine, gamma-aminobutyric acid or ATP was also excluded.

Effect of neutral alpha- and omega-amino acids and basic alpha-amino acids on uptake of L-histidine by intestinal mucosa, testis, spleen and kidney in vitro: a comparison with effect in brain

1. The effect of the D- and L-isomer of neutral alpha-amino acids, of omega-amino acids, and of basic L-alpha-amino acids on uptake of L-histidine in vitro has been investigated in intestinal mucosa, testis, spleen and kidney cortex, and compared with the effect in brain.2. Neutral alpha-amino acids produced inhibition that was in general greater the longer the carbon chain of the inhibiting amino acid. There were minor variations with different tissues.3. omega-amino acids produced little or no inhibition, with only slight variation between tissues. There was a tendency towards less inhibition the longer the carbon chain.4. The effect of basic amino acids varied with different tissues. With one exception, all produced significant inhibition with intestinal mucosa and testis. With spleen and kidney, inhibition was slight or absent, and resembled the effect produced by the omega-amino acids. With brain (previously reported elsewhere) the short-chain amino acids produced considerable inhibition, those having longer carbon chains little or none.5. Proline produced significant inhibition in brain and spleen, but none in the other tissues. Tryptophan had no effect with kidney.6. The findings are considered as further evidence for a relation between the extent to which an amino acid can be taken up by a given tissue and the specificity of the transport systems in that tissue. They also support the view that the nature of certain transport systems may vary considerably between different tissues.