Mechanisms of glutamine transport in rat adipocytes and acute regulation by cell swelling.
Adipose tissue is a major site for whole-body glutamine synthesis and we are investigating mechanisms and regulation of glutamine transport across the adipocyte membrane. Glutamine transport in adipocytes includes both high- and low-affinity Na+-dependent components (consistent with observed expression of ASCT2 and ATA2/SAT2 transporter mRNAs respectively) and a Na+-independent transport component (consistent with observed expression of LAT1/2 transporter mRNAs). Hypo-osmotic (235 mosmol/kg) swelling of adipocytes transiently stimulated glutamine uptake (180% increase at 0.05 mM glutamine) within 5 mins. Stimulation was blocked by the tyrosine kinase inhibitor genistein and the MAP kinase pathway inhibitors PD98059 and SB203580, but not by wortmannin (PI 3-kinase inhibitor) or rapamycin (mTOR pathway inhibitor). Cell-swelling also stimulated uptake of glucose but not MeAIB (indicating that ASCT2 rather than ATA2 was stimulated by swelling). Insulin (66 nM) treatment for up to 1 h stimulated Na+-dependent glutamine transport and increased adipocyte water space. Activation of the ERK1-2 MAP kinase pathway by cell swelling or insulin may be important for rapid activation of the ASCT2 glutamine transporter in adipocytes. Insulin may also exert a minor additional stimulatory effect on adipocyte glutamine transport indirectly via cell swelling. The mechanisms regulating glutamine transport in adipose tissue are distinct from those in other major sites of glutamine turnover in the body (notably liver and skeletal muscle).
Ritchie
J W
JW
Division of Molecular Physiology, School of Life Sciences, Universtiy of Dundee, Scotland, United Kingdom.
Baird
F E
FE
Christie
G R
GR
Stewart
A
A
Low
S Y
SY
Hundal
H S
HS
Taylor
P M
PM
D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D026924:Amino Acid Transport System A / Q000235:genetics / Q000378:metabolism; D026962:Amino Acid Transport System ASC / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001834:Body Water / Q000378:metabolism; D048429:Cell Size; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D015778:Minor Histocompatibility Antigens; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009994:Osmolar Concentration; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley
D026924:Amino Acid Transport System A; D026962:Amino Acid Transport System ASC; D004791:Enzyme Inhibitors; D007328:Insulin; D015778:Minor Histocompatibility Antigens; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; C498849:Slc1a5 protein, rat; C412568:Slc38a2 protein, rat; D005973:Glutamine; D011505:Protein-Tyrosine Kinases; D020928:Mitogen-Activated Protein Kinases