Efflux Of Free Amino Acids Research Articles

An attenuated rate of leg muscle protein depletion and leg free amino acid efflux over time is seen in ICU long-stayers

BackgroundThere is extensive documentation on skeletal muscle protein depletion during the initial phase of critical illness. However, for intensive care unit (ICU) long-stayers, objective data are very limited. In this study, we examined skeletal muscle protein and amino acid turnover in patients with a prolonged ICU stay.MethodsPatients (n = 20) were studied serially every 8–12 days between days 10 and 40 of their ICU stay as long as patients stayed in the ICU. Leg muscle protein turnover was assessed by measurements of phenylalanine kinetics, for which we employed a stable isotope-labeled phenylalanine together with two-pool and three-pool models for calculations, and results were expressed per 100 ml of leg volume. In addition, leg muscle amino acid flux was studied.ResultsThe negative leg muscle protein net balance seen on days 10–20 of the ICU stay disappeared by days 30–40 (p = 0.012). This was attributable mainly to an increase in the de novo protein synthesis rate (p = 0.007). It was accompanied by an attenuated efflux of free amino acids from the leg. Leg muscle protein breakdown rates stayed unaltered (p = 0.48), as did the efflux of 3-methylhistidine. The arterial plasma concentrations of free amino acids did not change over the course of the study.ConclusionsIn critically ill patients with sustained organ failure and in need of a prolonged ICU stay, the initial high rate of skeletal muscle protein depletion was attenuated over time. The distinction between the acute phase and a more prolonged and more stable phase concerning skeletal muscle protein turnover must be considered in study protocols as well as in clinical practice.Trial registrationAustralian New Zealand Trial Registry, ACTRN12616001012460. Retrospectively registered on 1 August 2016.

Utilization of 15N-labelled yeast hydrolysate in Lactococcus lactis IL1403 culture indicates co-consumption of peptide-bound and free amino acids with simultaneous efflux of free amino acids

Lactococcus lactis subsp. lactis IL1403 was grown in medium containing unlabelled free amino acids and (15)N-labelled yeast hydrolysate to gain insight into the role of peptides as a source of amino acids under conditions where free amino acids are abundant. A mathematical model was composed to estimate the fluxes of free and peptide-derived amino acids into and out of the intracellular amino acid pool. We observed co-consumption of peptides and free amino acids and a considerable efflux of most free amino acids during growth. We did not observe significant differences between the peptide consumption patterns of essential and non-essential amino acids, which suggests that the incorporation of a particular amino acid is more dependent on its availability in a readily assimilated form than the organism's auxotrophy for it. For most amino acids the contribution of peptide-bound forms to the formation of biomass was initially between 30 and 60 % with the remainder originating from free amino acids. During the later stages of fermentation we observed a decrease in the utilization of peptide-bound amino acids, thus indicating that the more readily assimilated peptides are gradually exhausted from the medium during growth.

RBC deformability and amino acid concentrations after hypo-osmotic challenge may reflect chronic cell hydration status in healthy young men

Biomarkers of chronic cell hydration status are needed to determine whether chronic hyperosmotic stress increases chronic disease risk in population-representative samples. In vitro, cells adapt to chronic hyperosmotic stress by upregulating protein breakdown to counter the osmotic gradient with higher intracellular amino acid concentrations. If cells are subsequently exposed to hypo-osmotic conditions, the adaptation results in excess cell swelling and/or efflux of free amino acids. This study explored whether increased red blood cell (RBC) swelling and/or plasma or urine amino acid concentrations after hypo-osmotic challenge might be informative about relative chronic hyperosmotic stress in free-living men. Five healthy men (20–25 years) with baseline total water intake below 2 L/day participated in an 8-week clinical study: four 2-week periods in a U-shaped A-B-C-A design. Intake of drinking water was increased by +0.8 ± 0.3 L/day in period 2, and +1.5 ± 0.3 L/day in period 3, and returned to baseline intake (0.4 ± 0.2 L/day) in period 4. Each week, fasting blood and urine were collected after a 750 mL bolus of drinking water, following overnight water restriction. The periods of higher water intake were associated with significant decreases in RBC deformability (index of cell swelling), plasma histidine, urine arginine, and urine glutamic acid. After 4 weeks of higher water intake, four out of five participants had ½ maximal RBC deformability below 400 mmol/kg; plasma histidine below 100 μmol/L; and/or undetectable urine arginine and urine glutamic acid concentrations. Work is warranted to pursue RBC deformability and amino acid concentrations after hypo-osmotic challenge as possible biomarkers of chronic cell hydration.

Effect of salinity change on free amino acid content in Pacific oyster

: In order to identify free amino acids (FAA) that are importantas intracellular osmolytes in Crassostrea gigas, we investigatedthe change in FAA content in the mantle exposed to an abrupt decreaseor increase in salinity. In hypo-osmotic adaptation, most FAA showedremarkable and synchronous decreases from 2 to 8 h, suggestingthat the non-selective efflux of FAA was mainly responsible forthe decrease in FAA. Taurine that accounted for approximately 80% oftotal FAA content contributed most significantly to the hypo-osmoticadaptation. In hyper-osmotic adaptation, significant increases inglycine, alanine, β-alanine, proline, arginine and taurinewere observed. Of these, alanine showed an immediate increase thatis important to short-term adaptation to hyper-osmolality, whiletaurine showed a slower and substantial increase that contributesto a long-term adaptation to hyper-osmolality.

Amino Acid Cycling in Colonies of the Planktonic Marine Cyanobacterium Trichodesmium thiebautii

We examined diel trends in internal pools and net efflux of free amino acids in colonies of the nonheterocystous, diazotrophic cyanobacterium Trichodesmium thiebautii, freshly collected from waters of the Caribbean and the Bahamas. The kinetics of glutamate uptake by whole colonies were also examined. While intracolonial pools of most free amino acids were relatively constant through the day, pools of glutamate and glutamine varied over the diel cycle, with maxima during the early afternoon. This paralleled the daily cycle of nitrogenase activity. We also observed a large net release of these two amino acids from intact colonies. Glutamate release was typically 100 pmol of N colony h. This is about one-fourth the concurrent rate of N(2) fixation during the day. However, while nitrogenase activity only occurs during the day, net release of glutamate and glutamine persisted into the night and may therefore account for a greater loss of recently fixed N on a daily basis. This release may be an important route of new N input into tropical, oligotrophic waters. Whole colonies also displayed saturation kinetics with respect to glutamate uptake. The K(s) for whole colonies varied from 1.6 to 3.2 muM, or about 100-fold greater than typical ambient concentrations. Thus, uptake systems appear to be adapted to the higher concentrations of glutamate found within the intracellular spaces of the colonies. This suggests that glutamate may be a vehicle for N exchange among trichomes in the colony.

The mechanism of crustacean salinity tolerance: Cell volume regulation by K+ and glycine effluxes

The regulation of muscle fiber K+ and free amino acid (FAA) concentrations during hypoosmotic stress was investigated in the moderately euryhaline crab Cancer irroratus. After 6 h of exposure to 60% ASW, muscle fiber K+ concentration declined from 185 mM to 140 mM. Following this, the blood glycine levels began to increase, indicating an FAA efflux from the cells. These data indicate that both muscle fiber K+ and FAA contribute to cell volume regulation in C. irroratus. The early release of K+ limits the initial rate of cell hydration. The subsequent efflux of glycine accounts for the volume regulation response of the muscle fibers. The cell volume regulatory system of C. irroratus is a coordinated use of both inorganic ions and FAA.

Free amino acid mediated volume regulation of isolatedNoetia ponderosa red blood cells: Control by Ca2+ and ATP

The ionic and metabolic requirements of cellular volume regulation and the free amino acid (FAA) efflux from hypoosmotically stressedNoetia ponderosa (Mollusca: Arcidae) red blood cells was studied. Deletion of Ca2+ from 50% ASW prevented cell volume regulation and decreased the FAA efflux. Addition of Co2+, Mn2+, or La3+ to 50% ASW increased volume regulation and the FAA efflux, while verapamil, a Ca2+ antagonist, inhibited volume regulation and the FAA efflux. Volume regulation by the blood cells has a metabolic component also since DNP or incubation of the cells at 4°C both inhibited volume regulation and the FAA efflux. Thus, the FAA permeability ofN. ponderosa blood cell membranes can be manipulated by altering seawater [Ca2+] or by indirectly modifying intracellular levels of ATP.

Cellular volume regulation in salinity stressed molluscs: The response ofNoetia ponderosa (Arcidae) red blood cells to osmotic variation

Salinity stressed marine molluscs volumeregulate utilizing intracellular free amino acids. However, the actual changes in cell volume associated with free amino acid regulation are usually nerver measured or only indirectly measured since volume regulation has only been studied in whole animals or isolated tissues. The blood cells ofNoetia ponderosa (Mollusca: Arcidae) were used to specify the relationship between cell size changes and free amino acid permeability during volume regulation. Over the nonlethal salinity range,N. ponderosa is an osmotic conformer that volume regulates using free amino acids. Furthermore, when changes in blood cell size were measured with hematocrits, isolatedN. ponderosa blood cells placed into hypoosmotic seawater, volume regulated with a free amino acid efflux. Thus, the isolatedN. ponderosa blood cells provide a suitable preparation for studying the control of membrane amino acid permeability during volume regulation.

A correlation between the activity of divalent cation activated adenosine triphosphatase in the cell membrane and low salinity tolerance of the ribbed mussel, Modiolus demissus demissus

AbstractA comparison was made between the bound divalent cation stimulated adenosine triphosphatase (ATPase) activity of the cell membrane and the regulation of free amino‐acid (FAA) permeability in the myocardium of the bivalve (Modiolus demissus) during isosmotic and hypoosmotic stress. The FAA efflux induced by isosmotic, divalent cation free, artificial sea water (ASW) was reduced by Ca2+, Mg2+, Mn2+ and Co2+ at concentrations non‐lethal to the intact heart. However, the order of effectiveness in reducing the efflux was not the same as the effectiveness of the divalent cations on the stimulation of ATPase activity. In addition, ATPase activity with the concentrations of Ca2+ and Mg2+ in full strength ASW or in 50% ASW was inhibited by Co2+ and stimulated by Mn2+ Under isosmotic conditions, modification of ATPase activity by Co2+ or Mn2+ did not alter FAA permeability. However, during hypoosmotic stress, the recovery of normal FAA permeability correlated with divalent cation activated ATPase activity; increased enzyme activity in the presence of Mn2+ was coincident with a decreased FAA efflux and decreased enzyme activity in the presence of Co2+ accompanied an increased FAA efflux.Therefore, the recovery of normal FAA permeability during a hypoosmotic stress is correlated with divalent ATPase activity. During isosmotic conditions, FAA permeability may be controlled by divalent cation binding.