Discrimination of Single Transport Systems

Inui, Yukiharu; Christensen, Halvor N.

doi:10.1085/jgp.50.1.203

Cited by 159 publications

(38 citation statements)

References 13 publications

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“…5) The experiments reported here provide evidence for a Na+-gradient-stimulated, electrogenic mechanism of iso-Abu uptake (24) in membranes from untransformed and SV40-transformed mouse fibroblasts. Observations that iso-Abu uptake against its concentration gradient could be driven by transmembrane Na+ gradients imposed independently of (Na+ + K+)ATPase activity, and that flux of iso-Abu in either direction across the membrane was decreased by Na+ added to the opposite side, support a type of Na+-gradient-coupled mechanism proposed by Crane (25).…”

Section: Comparison Of Iso-abu Carrier Activity Of Isolated Membranesmentioning

confidence: 59%

Regulation of active alpha-aminoisobutyric acid transport expressed in membrane vesicles from mouse fibroblasts.

Lever¹

1976

Proc. Natl. Acad. Sci. U.S.A.

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Membrane vesicles isolated from untransformed Balb/c and Swiss mouse fibroblasts and from those transformed by simian virus 40 catalyzed carrier-mediated uptake of L-a-aminoisobutyric acid. Concentrative uptake required the presence of a Na+ gradient (external Na+ > internal Na+) and occurred independently of endogenous (Na+ + K+) ATPase activity. This process is electrogenic, since uptake was stimulated by a K+ diffusion gradient (internal > external) in the presence of valinomycin or by the addition of the Na+ salt of a permeant ion, conditions expected to create an interiornegative membrane potential. Both the initial rate of concentrative uptake of L-a-aminoisobutyric acid and its maximal accumulation, driven by a standard Na+ gradient, were decreased in vesicles from density-inhibited, untransformed cells and increased in those from cells transformed by simian virus 40 compared with vesicles from proliferating untransformed cells. An increased maximal velocity ( Vm) of uptake stimulated by Na+ gradient was observed in vesicles from transformed cells compared with those from untransformed cells, suggesting an increase in the number of carriers or in their mobility. Since the relative extent of accumulation of this model amino acid driven by a standard Na+ gradient also differed with growth or transformed status, an additional possibility for cellular regulation of this process could be alteration of membrane Na+ permeability or carrier response to Na+. Alterations in nutrient uptake activity that accompany changes in cellular proliferation rate of untransformed mouse fibroblasts induced by serum, hormones, or viral transformation (1) have been implicated in models of cell cycle control involving regulation of surface membrane functions (2, 3). However, studies of regulation of nutrient uptake using intact cells have been unable to distinguish unambiguously between effects of intracellular metabolic changes, changes associated with the plasma membrane, and effects of surface area and cell overlap on uptake rates. In certain cases, even the use of nonmetabolizable analogues does not permit specific assessment of the locus of regulation of uptake activity. For example, the activity of the Na+ and K+ transport system in fibroblasts, expressed enzymatically as a (Na+ + K+)ATPase, is altered by cell density and proliferation rate (4), serum and purified growth-promoting agents (5), and viral transformation (6). Thus, the rate of Na+-dependent, ouabain-sensitive a-aminoisobutyric acid (iso-Abu) uptake (7) could reflect this observed regulation of the Na+ pump activity rather than alteration of the amino acid carriers.In this report, these possibilities are investigated using sealed membrane vesicles with transport catalytic activity, isolated from mouse fibroblasts. Evidence for Na+ gradient-stimulated, electrogenic, concentrative iso-Abu uptake was obtained, as recently described for intestinal brush border membranes (8) and Ehrlich ascites cell membranes (9). By use of transvesicular Na+ gradients maintai...

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Section: Comparison Of Iso-abu Carrier Activity Of Isolated Membranesmentioning

confidence: 59%

Regulation of active alpha-aminoisobutyric acid transport expressed in membrane vesicles from mouse fibroblasts.

Lever¹

1976

Proc. Natl. Acad. Sci. U.S.A.

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“…(Inui & Christensen, 1966) gave straight lines with intercepts on the ordinate of 1-22 + 0-17 for methionine and 3-16 + 0-76 for lysine. The value of 1-22, which is not significantly different from 1, confirms that all alanine uptake can be inhibited by high concentrations ofmethionine.…”

Section: Resultsmentioning

confidence: 96%

Distinguishing transport systems having overlapping specificities for neutral and basic amino acids in the rabbit ileum.

Paterson¹,

Sepúlveda²,

Smith³

1981

The Journal of Physiology

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SUMMARY1. The kinetic parameters of lysine and alanine uptake by rabbit ileal mucosa have been measured in the presence and absence of Na.2. Using lysine as an inhibitor of part of alanine uptake in the absence of Na it has been possible to define two mediated systems for alanine entry. One of these systems (Km 14-2 mM; Jmax 41-3 n-mole cm-2 min') is inhibited by lysine (Ki 0-96 mM) while the other (Km 115 mM; Jmax 323 n-mole cm-2 min') is not.3. Methionine is an effective inhibitor of both Na-independent uptake mechanisms for alanine.4. Na-independent lysine uptake also takes place through two mediated systems.

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“…Of the two C. A. CHIN AND D. M. K. LAM major systems, A (alanine-preferring) and L (leucine-preferring), involved in the transport of the neutral amino acids into most tissues, glycine has been shown to enter cells predominantly through system A (Oxender & Christensen, 1963;Inui & Christensen, 1966;Sepulveda & Smith, 1978). To determine if glycine uptake in the goldfish retina also enters through these systems, retinae were incubated with [3H]- glycine in the presence of 5 mm each alanine, proline and serine, or isoleucine, methionine and valine to inhibit system A or L respectively.…”

Section: Kinetics Of [3h]glycine Uptakementioning

confidence: 99%

The uptake and release of [3H]glycine in the goldfish retina.

Chin¹,

Lam²

1980

The Journal of Physiology

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2. The high-affinity mechanism, and probably also the low-affinity mechanism, is temperature-and Na+-dependent.3. The low-affinity mechanism for glycine uptake is not affected by 5 mM-isoleucine, methionine and valine in the medium. However, it is inhibited more than 90 % by 5 mM-alanine, proline and serine in the medium. This result indicates that the low-affinity transport for glycine may go through system A of the neutral amino acid transport system which is present in most tissues to transport glycine and certain neutral amino acids for metabolic purposes.4. The high-affinity mechanism for glycine uptake is, however, not affected by the presence of up to 100-fold excess of all amino acids examined.5. Autoradiographic studies show that at least one type of amacrine cell and one type of probable interplexiform cell take up [3H]glycine both in the presence and absence of 5 mM-alanine, proline and serine, indicating that these neurones possess the high-affinity mechanism for glycine uptake.6.[3H]Glycine accumulated in the retina can be released by increasing the external K+ concentration. This release is probably Ca2+-dependent since it is blocked by 10 mM-Co2+ in the medium. Additionally, autoradiographic studies show that [3H]glycine taken up by the glycine-accumulating neurones can also be released by Ca2+-dependent, K+-depolarization of the retina.

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Discrimination of Single Transport Systems

Cited by 159 publications

References 13 publications

Regulation of active alpha-aminoisobutyric acid transport expressed in membrane vesicles from mouse fibroblasts.

Regulation of active alpha-aminoisobutyric acid transport expressed in membrane vesicles from mouse fibroblasts.

Distinguishing transport systems having overlapping specificities for neutral and basic amino acids in the rabbit ileum.

The uptake and release of [3H]glycine in the goldfish retina.

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