Regulatory mechanisms of SNAT2, an amino acid transporter, in L6 rat skeletal muscle cells by insulin, osmotic shock and amino acid deprivation

Several studies have demonstrated that the activity of system A is upregulated by insulin, osmotic shock and amino acid deprivation. However, the mechanisms are not clear. We carried out studies using L6 rat skeletal muscle cells to clarify the mechanisms of upregulation of system A activity by insulin, osmotic shock and amino acid deprivation. The upregulation was found to be due to an increase in Vmax, not Km. Chloroquine and wortmannin inhibited the upregulation induced by insulin stimulation and amino acid deprivation but not that induced by osmotic shock. On the other hand, cycloheximide and actinomycin D inhibited the upregulation by each stimulation. Moreover, PD98059 and SP600125 inhibited only amino acid deprivation-induced upregulation and SB202190 inhibited only insulin-induced upregulation. Our findings indicate that the mechanisms of upregulation of system A activity by insulin, osmotic shock and amino acid deprivation are different in L6 cells. Western blot and RT-PCR analysis showed an increase in system A at the protein and mRNA levels with each stimulation.