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The Journal of physiology1987; 389; 385-409; doi: 10.1113/jphysiol.1987.sp016662

Heterogeneity of amino acid transport in horse erythrocytes: a detailed kinetic analysis of inherited transport variation.

Abstract: 1. Thoroughbred horses were divisible into five distinct amino acid transport subgroups on the basis of their erythrocyte permeability to L-alanine, measured uptake rates ranging from 5 to 625 mumol l cells-1 h-1 (0.2 mM-extracellular L-alanine, 37 degrees C). 2. Erythrocytes from animals belonging to the lowest L-alanine permeability subgroup (5-15 mumol l cells-1 h-1) (transport-deficient type) exhibited slow nonsaturable transport of this amino acid. In contrast, cells from horses of the four transport-positive subgroups possessed additional high-affinity (apparent L-alanine Km (Michaelis constant) congruent to 0.3 mM) and/or low-affinity (apparent L-alanine Km congruent to 13 mM) Na+-independent transport routes selective for L-neutral amino acids of intermediate size. The two transporters, designated systems asc1 and asc2, respectively, also possessed a significant affinity for dibasic amino acids. 3. Amino acid transport activity in horse erythrocytes behaved as if controlled by three co-dominant alleles (s, h and l), where s is a silent allele, and h and l code for the functional presence of systems asc1 and asc2, respectively. 4. At physiological temperature, system asc1 operated preferentially in an exchange mode. In contrast, system asc2 did not participate in exchange reactions at 37 degrees C, but did exhibit significant trans-acceleration at 25 degrees C. 5. Reduction of the incubation temperature also resulted in dramatic decreases in apparent Km and Vmax for L-alanine uptake by system asc2, whereas the effects of temperature on system asc1 were much less marked. At 5 degrees C the two transporters exhibited equivalent kinetic constants for L-alanine influx. L-Alanine uptake by transport-deficient cells was relatively insensitive to temperature. Influx by this route may represent the ground-state permeability of the lipid bilayer. 6. The effects of low temperature on system asc2 suggest a preferential impairment of the mobility of the unloaded carrier relative to that of the loaded transporter. Similarly, the different kinetic properties of systems asc1 and asc2 at physiological temperature are attributed to a difference in the mobilities of the empty carriers, this difference being minimized at 5 degrees C.
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Publication Date: 1987-08-01 PubMed ID: 3681732PubMed Central: PMC1192086DOI: 10.1113/jphysiol.1987.sp016662Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The study investigates the varied levels of amino acid transport in the red blood cells of thoroughbred horses, identifying five distinctive subgroups. Key factors examined within the transport process include the permeability to L-alanine, temperature effects, and the functionality of transport systems asc1 and asc2.

Identifying Subgroups in Amino Acid Transport

  • Thoroughbred horses were divided into five unique subgroups based on the permeability of their red blood cells to L-alanine, a crucial amino acid.
  • The study found that the uptake rates varied significantly from 5 to 625 micromol per liter of cells per hour when tested with 0.2 mM-extracellular L-alanine at 37 degrees Celsius.

Contrasting Transport Activities

  • Erythrocytes (types of red blood cells) from horses within the subgroup showing the lowest permeability to L-alanine had a slower non-saturable transport of this particular amino acid.
  • On the other hand, erythrocytes from horses in the four other subgroups that showed positive permeability possessed additional high- and low-affinity transport pathways for L-neutral amino acids of intermediate size.
  • They utilized two systems, asc1 and asc2, to transport amino acids. These transporters also demonstrated significant affinity for dibasic amino acids.

Temperature Effects on Transport System

  • System asc1 mostly functioned as an exchange mode at physiological temperature.
  • On the contrary, system asc2 did not participate in exchange reactions at 37 degrees Celsius, but at 25 degrees Celsius, it showed significant trans-acceleration.
  • Cold incubation temperatures dramatically reduced the L-alanine uptake by system asc2, while the effect on system asc1 remains relatively less.

Control of Amino Acid Transport Activity

  • According to the study, transportation activity in horse red blood cells was controlled by three co-dominant alleles (s, h, and l). ‘s’ allele was silent, while ‘h’ and ‘l’ coded for the functional presence of systems asc1 and asc2 respectively.

Implications of Findings

  • Experimental findings suggest a difference in mobilities of the empty carriers at physiological temperature, which get minimized at 5 degrees Celsius. This may explain the differential kinetic properties of systems asc1 and asc2.
  • Understanding these variations can help identify the unique transport properties for different groups of horses. This potentially has important ramifications for horse health and therapeutic interventions.

Cite This Article

APA
Fincham DA, Mason DK, Paterson JY, Young JD. (1987). Heterogeneity of amino acid transport in horse erythrocytes: a detailed kinetic analysis of inherited transport variation. J Physiol, 389, 385-409. https://doi.org/10.1113/jphysiol.1987.sp016662

Publication

The Journal of physiology
ISSN: 0022-3751
NlmUniqueID: 0266262
Country: England
Language: English
Volume: 389
Pages: 385-409

Researcher Affiliations

Fincham, D A
  • Department of Biochemistry, Faculty of Medicine, Chinese University of Hong Kong, Shatin, N.T.
Mason, D K
    Paterson, J Y
      Young, J D

        MeSH Terms

        • Alanine / metabolism
        • Amino Acids / blood
        • Amino Acids / pharmacology
        • Animals
        • Biological Transport / drug effects
        • Cell Membrane Permeability
        • Erythrocytes / metabolism
        • Horses / blood
        • Kinetics

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        Citations

        This article has been cited 5 times.
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