Effect of monensin on 2-deoxyglucose uptake, the insulin receptor and phosphatidylinositol 3-kinase activity in rat muscle.
Preincubation of rat soleus muscle with 1 and 10 microM monensin for 2 h increased the subsequent basal 2-deoxyglucose uptake by muscle 76 and 121% respectively. Under the same conditions, monensin decreased the insulin-stimulated (1 mU/ml) 2-deoxyglucose uptake by 29 and 37% respectively. The monensin-induced augmentation of basal 2-deoxyglucose uptake was inhibited 92% by cytochalasin B suggesting that the uptake is mediated by glucose transporters. Monensin did not increase the cellular accumulation of L-glucose in muscle indicating that it does not affect the cell membrane integrity. Neither the stimulatory effect of monensin on basal 2-deoxyglucose uptake nor the opposite, inhibitory action of monensin on the insulin-stimulated 2-deoxyglucose uptake were influenced by the removal of Ca2+ from the medium or by dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum, suggesting that the actions of monensin are not mediated by calcium. Monensin had no effect on muscle ATP concentration. The monensin-induced augmentation of basal 2-deoxyglucose uptake was neither associated with stimulation of muscle phosphatidylinositol 3-kinase activity nor inhibited by wortmannin, demonstrating that the increase in basal 2-deoxyglucose uptake is not mediated by activation of phosphatidylinositol 3-kinase. The inhibition of insulin-stimulated 2-deoxyglucose uptake by monensin was associated with a 31% decrease in the abundance of insulin receptors in muscles, a 64% decrease in the insulin-induced autophosphorylation of the insulin receptor beta-subunit, and a 44% reduction of the insulin-stimulated phosphatidylinositol 3-kinase activity. Addition of monensin into the phosphatidylinositol 3-kinase reaction had no effect on the activity of the enzyme, demonstrating that the inhibition in monensin-treated muscles is indirect and occurs upstream of phosphatidylinositol 3-kinase. It is concluded that monensin has a dual effect on 2-deoxyglucose uptake by skeletal muscle: it stimulates basal uptake but inhibits the insulin-stimulated uptake. The primary cause of the latter, inhibitory effect of monensin is at the level of the insulin receptor.
Turinsky
J
J
Department of Physiology and Cell Biology, Albany Medical College, New York 12208, USA.
Damrau-Abney
A
A
Elmendorf
J S
JS
Smith
T R
TR
D000255:Adenosine Triphosphate / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D003571:Cytochalasin B / Q000494:pharmacology; D003620:Dantrolene / Q000494:pharmacology; D003847:Deoxyglucose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D007329:Insulin Antagonists / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology*; D008297:Male; D008985:Monensin / Q000494:pharmacology*; D009125:Muscle Relaxants, Central / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013268:Stimulation, Chemical; D000077191:Wortmannin
D000730:Androstadienes; D007328:Insulin; D007329:Insulin Antagonists; D007476:Ionophores; D009125:Muscle Relaxants, Central; D003571:Cytochalasin B; D000255:Adenosine Triphosphate; D008985:Monensin; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011972:Receptor, Insulin; D003620:Dantrolene; D005947:Glucose; D000077191:Wortmannin