The T-tubule is a cell-surface target for insulin-regulated recycling of membrane proteins in skeletal muscle

• Published in: Biochemical journal 1995-12, Vol.312 ( Pt 2) (2), p.393-400
• Main Authors: Muñoz, P, Rosemblatt, M, Testar, X, Palacín, M, Thoidis, G, Pilch, P F, Zorzano, A
• Format: Article
• Language: English
• Subjects: Animals; Calcium Channels - isolation & purification; Calcium Channels - metabolism; Calcium Channels, L-Type; Carrier Proteins - analysis; Carrier Proteins - metabolism; Cell Fractionation; Glucose Transporter Type 4; Insulin - pharmacology; Male; Membrane Proteins - metabolism; Monosaccharide Transport Proteins - analysis; Monosaccharide Transport Proteins - metabolism; Muscle Proteins; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Organelles - metabolism; Rats; Rats, Wistar; Receptor, Insulin - isolation & purification; Receptor, Insulin - metabolism; Sarcolemma - metabolism
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj3120393

(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.