Energetics of Na+-dependent amino acid co-transport in Ehrlich ascites tumor cells

Wd, Dawson; Tc, Smith

doi:10.1016/0005-2736(87)90309-9

Cited by 14 publications

(9 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…During hyperinsulinemia, there was a change in potassium balance, reflecting in all likelihood an increase in Na,K-ATPase activity (30,32,50) and hyperpolarization of plasma membrane (52) accompanied by a steeper electrochemical sodium gradient across the cell membrane. Because amino acid transport by system A is coupled to Na+ transport (24,25), hyperpolarization of the cell membrane and enhanced Na+ influx would be expected to augment the inward transport of system A transported amino acids (53). Conversely, a decrease in intracellular sodium activity might be expected to decrease the outward flux ofamino acids.…”

Section: Resultsmentioning

confidence: 99%

Effect of insulin on system A amino acid transport in human skeletal muscle.

Bonadonna¹,

Saccomani²,

Cobelli³

et al. 1993

J. Clin. Invest.

View full text Add to dashboard Cite

IntroductionTransmembrane transport of neutral amino acids in skeletal muscle is mediated by at least four different systems (system A, ASC, L, and N'), and may be an important target for insulin's effects on amino acid and protein metabolism. We have measured net amino acid exchanges and fractional rates of inward (ki, min') and outward (k*ot, min-) transmembrane transport of 2-methylaminoisobutyric acid (MeAIB, a nonmetabolizable amino acid analogue, specific for system A amino acid transport) in forearm deep tissues (skeletal muscle), by combining the forearm perfusion technique and a novel dual tracer ([1-H3J-D-mannitol and 2-[1-'4CJ-methylaminoisobutyric acid) approach for measuring in vivo the activity of system A amino acid transport. Seven healthy lean subjects were studied. After a baseline period, insulin was infused into the brachial artery to achieve local physiologic hyperinsulinemia (76±8,uU/ml vs 6.4±1.6 ,U/ml in the basal period, P < 0.01) without affecting systemic hormone and substrate concentrations. Insulin switched forearm amino acid exchange from a net output (-2,630±1,100 nmol/min per kg of forearm tissue) to a net uptake (1,610±600 nmol/min per kg, P < 0.01 vs baseline). Phenylalanine and tyrosine balances simultaneously shifted from a net output (-146±47 and -173±34 nmol/min per kg, respectively) to a zero balance (163±51 for phenylalanine and 15.5±14.3 nmol/min per kg for tyrosine, P < 0.01 vs baseline for both), showing that protein synthesis and breakdown were in equilibrium during hyperinsulinemia. Net negative balances of alanine, methionine, glycine, threonine and asparagine (typical substrates for system A amino acid transport) also were decreased by insulin, whereas serine (another substrate for system A transport) shifted from a zero balance to net uptake. Insulin increased kih of MeAIB from a basal value of 11.8 10-2+17 102. min to 13.7 10-2+2.10-2-min-I (P < 0.02 vs the postabsorptive value), whereas k.. was unchanged. We conclude that physiologic hyperinsulinemia stimulates the activity of system A amino acid transport in human skeletal muscle, and that this effect may play a role in determining the overall concomitant response of muscle amino acid/protein metabolism to insulin. (J. Clin. Invest. 1993. 91:514-521.) Key words: limb balance -2-methylaminoisobutyric acid -first-pass kinetics * protein turnover

show abstract

Section: Resultsmentioning

confidence: 99%

Effect of insulin on system A amino acid transport in human skeletal muscle.

Bonadonna¹,

Saccomani²,

Cobelli³

et al. 1993

J. Clin. Invest.

View full text Add to dashboard Cite

show abstract

“…However, it should be noted that prolonged incubations of dilute cell suspensions with the concomitant depletion of cellular amino acid content leads to indirect estimates of Vm which more closely approximate those obtained using microelectrodes (Laris et al, 1976(Laris et al, , 1978. Simple differences in incubation conditions cannot account completely for the observed disparity, however, since direct measurements of the steadystate Vm in the presence and absence of 2-aminoisobutyric acid (A1B) show no sustained depolarization (Dawson & Smith, 1987). At present the basis for the differences in the results fi'om these approaches remains unresolved.…”

Section: Introductionmentioning

confidence: 89%

“…This assumes that the ion activity coefficients for K + (TK) are identical in the two compartments. We have recently determined aK(Cell) using ion-selective electrodes (Dawson & Smith, 1987) and found it to be only about 56% that expected from chemical estimates (y~?" = 0.41 -+ 0.05 ellV versus YK = 0.73).…”

Section: Vm = Vk = -(Rt/f) Ln{ak(cell)/ak(env)}mentioning

confidence: 94%

“…Through its contribution to the ion electrochemical gradients, the potential serves as a source of energy for the uptake of certain amino acids (Lads et al, 1976;Philo & Eddy, 1978;Hacking & Eddy, 1981;Dawson & Smith, 19871. Conversely, activation of amino acid transport leads to membrane depolarization, consistent with stimulation of rheogenic Na + entry through the cotransport system (Henius & Laris, 1979;Hacking & Eddy, 1981;Dawson & Smith, 1987). This depolarization is transient unless active Na+/K + transport is inhibited, suggesting that the subsequent activation of the Na + pump is electrogenic (Dawson & Smith, 19871.…”

Section: Introductionmentioning

confidence: 93%

“…Ehrlich cells maintain nonequilibrium distributions of Na + and K + across the cell membrane by coupling their transport to cellular metabolism (Hempling, 1958;Maizels et al, 1958). In addition, the energy available from the ion gradients is 0 utilized to permit cellular accumulation of the Na +-dependent amino acid o~-methylaminoisobutyric acid (MeAIB) (Philo & Eddy, 1978;Hacking & Eddy, 1981;Dawson & Smith, 1987). The ability of the cells to maintain the normal cation gradients and the capacity to concentrate MeAIB thus provide a sensitive measure of normal cell function.…”

Section: Uptake and Accumulation Of [14c]scn By Ehrlich Cellsmentioning

confidence: 99%

See 2 more Smart Citations

Validation of the use of the lipophilic thiocyanate anion for the determination of membrane potential in Ehrlich ascites tumor cells

Smith

Robinson

1989

J. Membrain Biol.

Self Cite

View full text Add to dashboard Cite

The utility of the lipophilic anion thiocyanate (SCN-) as a probe for the indirect estimation of the cell membrane potential (Vm) in Ehrlich ascites tumor cells has been evaluated by comparison to direct electrophysiological measurements. SCN accumulation is consistent with first-order uptake into a single, kinetically-identifiable cellular compartment, achieving steady-state distribution in 20-30 min at 22 degrees C. The steady state distribution ratio ([SCN-]e/[SCN-]e) in physiological saline is 0.44 +/- 0.02. Treatment of the cells with propranolol (0.13 mM), an activator of Ca2+ dependent K+ channels, reduces the steady-state distribution ratio to 0.19 +/- 0.02. Conversely, treatment with BaCl2 (10 mM), an antagonist of the pathway, increases the SCN- distribution ratio to 0.62 +/- 0.01. The equilibrium potentials (VSCN) calculated under these conditions are virtually identical to direct electrophysiological measurements of the Vm made under the same conditions. The effect of varying extracellular [K+] ([K+]e) in the presence of constant [Na+]e = 100 mM has also been tested. In control cells, elevation of [K+]e from 6 to 60 mM reduces VSCN from -20.6 +/- 1.0 to -13.2 +/- 1.2 mV. Again, microelectrode measurements give excellent quantitative agreement. Propranolol increases the sensitivity of the cells to varying [K+]e, so that a 10-fold elevation reduces VSCN by approximately 31 mV. BaCl2 greatly reduces this response: a 10-fold elevation in [K+]e yielding only a 4-mV reduction in VSCN. It is concluded that the membrane potential of Ehrlich cells can be estimated accurately from SCN- distribution measurements.

show abstract

Energetic mechanism of system a amino acid transport in normal and transformed mouse fibroblasts

Leister

Schenerman

Racker

1988

Journal Cellular Physiology

View full text Add to dashboard Cite

Ouabain treatment (0.4 mM) of normal and transformed C3H-10T1/2 cells caused a progressive increase in 2-aminoisobutyrate (AIB) transport reaching a maximum after 16 to 18 h exposure. There was a virtually complete blockage of this stimulated rate when 3 microM cycloheximide (CHX) was added together with ouabain at T = 0. In the transformed cell, addition of CHX after 14 h had no effect; in the normal cell, it inhibited (ca. 50%) the final AIB transport rate achieved after 24 h. The t1/2 for reaching maximal activity (insensitive to CHX exposure) was thus shifted from 8 h in the transformed cell to 15 h in the normal cell. Since the rate of achieving maximal activity in the absence of CHX was about the same in the two cells, the shift in t1/2 in the presence of CHX suggests that the rate of degradation is more rapid in the normal cell. Following ouabain treatment, the apparent Km for Na+ was decreased in both cells. The Km returned to the basal level 1 h after ouabain removal in the normal cell, but remained low in the transformed cell during this time period. The stimulation of AIB transport following ouabain removal was largely abolished by a proton ionophore (1799), a lipophilic cation (tetraphenyl-phosphonium), or ouabain. These results suggest that, under the conditions of ouabain stress, there is a switch in the bioenergetic mechanism. The Na+/K+ pump and System A transporter appear to be linked and the membrane potential generated by the Na+/K+ pump activity becomes a major driving force for AIB uptake.

show abstract

Energetics of Na+-dependent amino acid co-transport in Ehrlich ascites tumor cells

Cited by 14 publications

References 19 publications

Effect of insulin on system A amino acid transport in human skeletal muscle.

Effect of insulin on system A amino acid transport in human skeletal muscle.

Validation of the use of the lipophilic thiocyanate anion for the determination of membrane potential in Ehrlich ascites tumor cells

Energetic mechanism of system a amino acid transport in normal and transformed mouse fibroblasts

Contact Info

Product

Resources

About