The T-tubule is a cell-surface target for insulin-regulated recycling of membrane proteins in skeletal muscle.
(1) In this study we have determined the distribution of various membrane proteins involved in insulin-activated glucose transport in T-tubules and in sarcolemma from rat skeletal muscle. Two independent experimental approaches were used to determine the presence of membrane proteins in T-tubules: (i) the purification of T-tubules free from sarcolemmal membranes by lectin agglutination, and (ii) T-tubule vesicle immunoadsorption. These methods confirmed that T-tubules from rat skeletal muscle were enriched with dihydropyridine receptors and tt28 protein and did not contain the sarcolemmal markers dystrophin or beta 1-integrin. Both types of experiments revealed an abundant content of GLUT4 glucose carriers, insulin receptors and SCAMPs (secretory carrier membrane proteins) in T-tubule membranes. (2) Acute administration in vivo of insulin caused an increased abundance of GLUT4 in T-tubules and sarcolemma. On the contrary, insulin led to a 50% reduction in insulin receptors present in T-tubules and in sarcolemma, demonstrating that insulin-induced insulin receptor internalization affects T-tubules in the muscle fibre. The alteration in the content of GLUT4 and insulin receptors in T-tubules was a consequence of insulin-induced redistribution of these proteins. SCAMPs also redistributed in muscle membranes in response to insulin. They were recruited by insulin from intracellular high-density fractions to intracellular lighter-density fractions and to the cell surface, showing a pattern of insulin-induced cellular redistribution distinct from those of GLUT4 and the insulin receptor. (3) In conclusion, the T-tubule is a cell-surface target for membrane proteins involved in recycling such as SCAMPs or for membrane proteins that acutely redistribute in response to insulin such as GLUT4 or insulin receptors.
Muñoz
P
P
Departament de Bioquímica i Fisiologia, Facultat de Biologia, Universitat de Barcelona, Spain.
Rosemblatt
M
M
Testar
X
X
Palacín
M
M
Thoidis
G
G
Pilch
P F
PF
Zorzano
A
A
D000818:Animals; D015220:Calcium Channels / Q000302:isolation & purification / Q000378:metabolism; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism*; D002458:Cell Fractionation; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000032:analysis / Q000378:metabolism*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000302:isolation & purification / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism*
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D011972:Receptor, Insulin