Table 1.

Effect of extracellular l-Gln starvation, pH, and SNAT2 inhibition with MeAIB on intracellular free amino acid profile in L6-G8C5 myotubes after 2-h incubationsa

ParameterComposition of the Medium
pH7.47.17.4 (Control)7.77.4
l-Gln (mmol/L)02222
MeAIB (mmol/L)000010
Amino acidConcentration in fresh MEM (μmol/L)Intracellular Free Amino Acid Concentration (nmol/mg protein)
l-AlaNil75.9 ± 2.171.3 ± 1.370.0 ± 1.769.3 ± 2.569.4 ± 1.6
l-Arg6005.23 ± 0.15c3.99 ± 0.08c4.68 ± 0.124.94 ± 0.113.38 ± 0.11c
l-AsnNil0.54 ± 0.05c1.28 ± 0.05c1.43 ± 0.051.34 ± 0.030.92 ± 0.02c
l-AspNil25.6 ± 1.3c37.4 ± 1.2c47.4 ± 1.547.0 ± 0.643.8 ± 0.7
l-Cys200bUDUDUDUDUD
l-GluNil28.3 ± 1.3c37.0 ± 0.8d42.2 ± 2.148.8 ± 3.0c38.8 ± 2.0
GlyNil13.1 ± 0.514.4 ± 0.5c12.1 ± 0.210.4 ± 0.2c12.9 ± 0.3
l-His2003.6 ± 0.2c1.2 ± 0.1c2.4 ± 0.32.7 ± 0.20.8 ± 0.1c
l-Ile4005.5 ± 0.2c2.5 ± 0.1c3.7 ± 0.23.9 ± 0.21.7 ± 0.1c
l-Lys400UDUDUDUDUD
l-Met1003.7 ± 0.3c1.2 ± 0.2d1.8 ± 0.32.3 ± 0.31.1 ± 0.2
l-Phe2004.39 ± 0.12c1.92 ± 0.08c2.82 ± 0.093.14 ± 0.071.29 ± 0.04c
l-ProNil1.5 ± 0.1c3.9 ± 0.33.4 ± 0.23.4 ± 0.22.4 ± 0.1c
l-SerNil1.81 ± 0.061.53 ± 0.061.60 ± 0.051.58 ± 0.061.29 ± 0.05c
l-Thr40036.1 ± 1.1c15.3 ± 0.5c20.2 ± 0.425.9 ± 0.4c9.4 ± 0.2c
l-Trp501.40 ± 0.05c0.69 ± 0.05c0.98 ± 0.051.01 ± 0.040.52 ± 0.02c
l-Tyr2004.79 ± 0.15c2.32 ± 0.38c3.12 ± 0.153.41 ± 0.141.42 ± 0.06c
l-Val4006.03 ± 0.19c3.06 ± 0.14c4.05 ± 0.194.32 ± 0.192.59 ± 0.08c
  • a Data for l-Gln and l-Leu are presented in Figure 1. Results from one experiment representative of four independent experiments are shown (n = 5 replicate culture wells for each treatment). Ala, alanine; Arg, arginine; Asn, asparagine; Asp, aspartic acid; Cys, cysteine; Glu, glutamic acid; Gly, glycine; His, histidine; Ile, isoleucine; Lys, lysine; MeAIB, methylaminoisobutyrate; MEM, Minimum Essential Medium; Met, methionine; Phe, phenylalanine; Pro, proline; Ser, serine; Thr, threonine; Trp, tryptophan; Tyr, tyrosine; Val, valine; UD, undetectable.

  • b Added as cystine.

  • c P < 0.05 versus pH 7.4 control.

  • d P < 0.05 versus pH 7.7.