Phosphatidylinositol 4-kinase, but not phosphatidylinositol 3-kinase, is present in GLUT4-containing vesicles isolated from rat skeletal muscle.
Insulin stimulates the rate of glucose transport into muscle and adipose cells by translocation of glucose transporter (GLUT4)-containing vesicles from an intracellular storage pool to the surface membrane. This event is mediated through the insulin receptor substrates (IRSs), which in turn activate phosphatidylinositol (PI) 3-kinase isoforms. It has been suggested that insulin causes attachment of PI 3-kinases to the intracellular GLUT4-containing vesicles in rat adipose cells. Furthermore, it has also been shown that GLUT4-containing vesicles in adipose cells contain a PI 4-kinase. In the present study we investigate whether GLUT4-containing vesicles isolated from rat skeletal muscle display PI 3-kinase and/or PI 4-kinase activities. Insulin stimulation caused a rapid increase (5-15-fold increase compared with control) in the intracellular cytosolic IRS-1-associated PI-3 kinase activity. This PI 3-kinase activity was also present in a membrane preparation containing the insulin-regulatable pool of GLUT4 transporters. However, when GLUT4-containing vesicles were isolated by immunoprecipitation from basal and insulin-stimulated (3 min) skeletal muscle, the vesicles displayed PI 4-kinase, but not PI 3-kinase, activity. Insulin did not regulate the PI 4-kinase activity in the GLUT4-containing vesicles. In conclusion, GLUT4-containing vesicles from rat skeletal muscle contain a PI 4-kinase, but not a PI 3-kinase. It is suggested that, in skeletal muscle, insulin causes activation of the IRS/PI 3-kinase complex in an intracellular membrane compartment associated closely with the GLUT4-containing vesicles, but not in the GLUT4-containing vesicles themselves.
Copenhagen Muscle Research Centre, August Krogh Institute, 13 Universitetsparken, DK-2100 Copenhagen, Denmark. Skristiansen@aki.ku.dk
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D019870:1-Phosphatidylinositol 4-Kinase / Q000187:drug effects / Q000378:metabolism*; D000241:Adenosine / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000032:analysis / Q000378:metabolism*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D011233:Precipitin Tests; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D000077191:Wortmannin
D000730:Androstadienes; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; C495694:Slc2a4 protein, rat; D019869:Phosphatidylinositol 3-Kinases; D019870:1-Phosphatidylinositol 4-Kinase; D000241:Adenosine; D000077191:Wortmannin