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Jiri Turinsky - One of the best experts on this subject based on the ideXlab platform.
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Effect of monensin on 2-Deoxyglucose uptake, the insulin receptor and phosphatidylinositol 3-kinase activity in rat muscle.
The Journal of endocrinology, 1997Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, Terry R. SmithAbstract: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.
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Sphingomyelinase stimulates 2-Deoxyglucose uptake by skeletal muscle.
The Biochemical journal, 1996Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, G W Nagel, T. R. SmithAbstract:The effects of sphingomyelinase, phosphorylcholine, N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide) and sphingosine on basal and insulin-stimulated cellular accumulation of 2-deoxy-D-glucose in rat soleus muscles were investigated. Preincubation of muscles with sphingomyelinase (100 or 200 m-units/ml) for 1 or 2 h augmented basal 2-Deoxyglucose uptake by 29-91%, and that at 0.1 and 1.0 m-unit of insulin/ml 32-82% and 19-25% respectively compared with control muscles studied at the same insulin concentrations. The sphingomyelinase-induced increase in basal and insulin-stimulated 2-Deoxyglucose uptake was inhibited by 91% by 70 microM cytochalasin B, suggesting that it involves glucose transporters. Sphingomyelinase had no effect on the cellular accumulation of L-glucose, which is not transported by glucose transporters. The sphingomyelinase-induced increase in 2-Deoxyglucose uptake could not be reproduced by preincubating the muscles with 50 microM phosphorylcholine, 50 microM C2-ceramide or 50 microM C6-ceramide. Preincubation of muscles with 50 microM sphingosine augmented basal 2-Deoxyglucose transport by 32%, but reduced the response to 0.1 and 1.0 m-unit of insulin/ml by 17 and 27% respectively. The stimulatory effect of sphingomyelinase on basal and insulin-induced 2-Deoxyglucose uptake was not influenced by either removal of Ca2+ from the incubation medium or dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum. This demonstrates that Ca2+ does not mediate the action of sphingomyelinase on 2-Deoxyglucose uptake. Sphingomyelinase also had no effect on basal and insulin-stimulated activities of insulin receptor tyrosine kinase and phosphatidylinositol 3-kinase. In addition, 1 and 5 microM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, failed to inhibit the sphingomyelinase-induced increase in 2-Deoxyglucose uptake. These results suggest that sphingomyelinase does not increase 2-Deoxyglucose uptake by stimulating the insulin receptor or the initial steps of the insulin-transduction pathway. The data suggest the possibility that sphingomyelinase increases basal and insulin-stimulated 2-Deoxyglucose uptake in skeletal muscle as the result of an unknown post-receptor effect.
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Insulin-Stimulated Phosphatidylinositol 3-Kinase Activity and 2-Deoxy-D-Glucose Uptake in Rat Skeletal Muscles
Biochemical and Biophysical Research Communications, 1995Co-Authors: Jeffrey S Elmendorf, Alice Damrau-abney, T. R. Smith, T.s. David, Jiri TurinskyAbstract:Abstract To date there is suggestive evidence that phosphatidylinositol 3-kinase participates in insulin-stimulated glucose transport. However, its involvement in skeletal muscle, a major site of insulin-stimulated glucose disposal, has not been addressed. Therefore, we tested the effects of wortmannin, a known inhibitor of phosphatidylinositol 3-kinase, on insulin-stimulated 2-Deoxyglucose uptake by rat soleus muscle in vitro. Wortmannin (1 μM) reversibly inhibited insulin-induced 2-Deoxyglucose uptake in soleus muscle by 44%. Inclusion of 5 μM wortmannin in the incubation medium completely abolished the insulin-induced increment in 2-Deoxyglucose uptake. In conclusion, the results are consistent with the concept that phosphatidylinositol 3-kinase plays a role in the insulin-signaling cascade linking insulin-receptor tyrosine kinase activation to glucose uptake in skeletal muscle.
Wolf Singer - One of the best experts on this subject based on the ideXlab platform.
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Monocularly induced 2-Deoxyglucose patterns in the visual cortex and lateral geniculate nucleus of the cat: I. Anaesthetized and paralysed animals.
The European journal of neuroscience, 1993Co-Authors: Siegrid Löwel, Wolf SingerAbstract:Extending previous investigations of the topographic relationship between ocular dominance and orientation columns in the cat visual cortex the two systems were visualized with transneuronally transported [3H]proline and with activity-dependent uptake of [14C]2-Deoxyglucose, respectively. In addition, we used the 2-Deoxyglucose method for a functional assay of both columnar systems. To this end, cats were injected with [3H]proline in the right eye. Two weeks later, they were stimulated monocularly through this eye by presenting contours of only a single orientation in the left and contours of many different orientations in the right visual hemifield while 2-Deoxyglucose was injected. The patterns of increased 2-Deoxyglucose uptake and of terminal labelling were analysed in flat-mount sections of the visual cortices and in frontal sections of the lateral geniculate nuclei. In the lateral geniculate nucleus, regions of increased 2-Deoxyglucose uptake are in register with the [3H]proline-labelled laminae of the open eye. In the visual cortex, the hemispheres stimulated with many different orientations showed a rather homogeneous accumulation of 2-Deoxyglucose over the entire extent and throughout all layers of area 17. The hemispheres stimulated with a single orientation displayed columnar patterns of orientation domains essentially similar to those obtained with binocular presentation of a single orientation. In particular and despite monocular stimulation, regions of increased 2-Deoxyglucose uptake were neither in register with the [3H]proline-labelled terminals of the increased 2-Deoxyglucose uptake were neither in register with the [3H]proline-labelled terminals of the stimulated eye in layer IV nor confined to columns of neural tissue above and below these terminals. The maximal horizontal offset between the termination sites of thalamic afferents and activated orientation columns was in the order of 400 microns. These findings suggest several conclusions. (i) In the cat visual cortex, binocular convergence seems to occur so early in cortical processing that monocular stimulation with many orientations leads to a rather homogeneous activation of cortical tissue. (ii) From the termination zones of geniculate afferents activity is apparently distributed already within layer IV to the respective orientation columns. (iii) This horizontal spread of activity could be assured by target cells with radially extending dendrites and/or tangentially oriented fibres.
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Monocularly Induced 2-Deoxyglucose Patterns in the Visual Cortex and Lateral Geniculate Nucleus of the Cat: II. Awake Animals and Strabismic Animals
European Journal of Neuroscience, 1993Co-Authors: Siegrid Löwel, Wolf SingerAbstract:In the course of experiments studying the organization of ocular dominance columns in the visual cortex of cats, we noticed that--contrary to common belief--labelling with 2-Deoxyglucose after monocular stimulation failed to induce a pattern of ocular dominance columns but resulted in a rather homogenous 2-Deoxyglucose uptake throughout area 17 in anaesthetized and paralysed animals. We wondered whether 2-Deoxyglucose columns could be obtained in awake animals and/or in strabismic animals, which have a more pronounced segregation of ocular dominance columns. To this end, we investigated 2-Deoxyglucose patterns after monocular stimulation in three groups of animals: (i) in awake normally reared cats, (ii) in awake strabismic cats and (iii) in anaesthetized and paralysed strabismic cats. Additionally, we labelled ocular dominance columns with intraocular [3H]proline injections. In all cats, monocular stimulation induced 2-Deoxyglucose patterns that were in precise register with the proline-labelled ocular dominance columns in layer IV. Regions of increased 2-Deoxyglucose uptake extended in a columnar fashion through all cortical layers. In contrast to normally reared animals, in strabismic cats, the expression of 2-Deoxyglucose labelled ocular dominance columns was not abolished by anaesthesia or paralysis. However, there was a difference between the 2-Deoxyglucose patterns in the awake normally reared cats and the strabismic animals. In the former, the patches of 2-Deoxyglucose labelling were smaller and occupied less territory than the afferents of the stimulated eye in layer IV. Together with the results of the previous study, these data indicate that in awake normally reared and in awake and anaesthetized strabismic cats, but not in anaesthetized and paralysed normally reared animals, monocular stimulation activates selectively neurons in columns that are in register with the termination sites of afferents from the stimulated eye. This suggests the existence of a mechanism in normally reared animals which restricts cortical activation after monocular stimulation to territories that are in register with the afferents from the stimulated eye. This mechanism appears to be effective only when the animals are awake and actively exploring their environment. This and the fact that the active columns were narrower than the terminal fields of the stimulated eye suggest an active inhibitory process, perhaps related to mechanisms of selective attention. The observation that ocular dominance columns persist in strabismic cats even under anaesthesia can be accounted for by the lack of binocular convergence in these animals.
Jeffrey S Elmendorf - One of the best experts on this subject based on the ideXlab platform.
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Effect of monensin on 2-Deoxyglucose uptake, the insulin receptor and phosphatidylinositol 3-kinase activity in rat muscle.
The Journal of endocrinology, 1997Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, Terry R. SmithAbstract: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.
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Sphingomyelinase stimulates 2-Deoxyglucose uptake by skeletal muscle.
The Biochemical journal, 1996Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, G W Nagel, T. R. SmithAbstract:The effects of sphingomyelinase, phosphorylcholine, N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide) and sphingosine on basal and insulin-stimulated cellular accumulation of 2-deoxy-D-glucose in rat soleus muscles were investigated. Preincubation of muscles with sphingomyelinase (100 or 200 m-units/ml) for 1 or 2 h augmented basal 2-Deoxyglucose uptake by 29-91%, and that at 0.1 and 1.0 m-unit of insulin/ml 32-82% and 19-25% respectively compared with control muscles studied at the same insulin concentrations. The sphingomyelinase-induced increase in basal and insulin-stimulated 2-Deoxyglucose uptake was inhibited by 91% by 70 microM cytochalasin B, suggesting that it involves glucose transporters. Sphingomyelinase had no effect on the cellular accumulation of L-glucose, which is not transported by glucose transporters. The sphingomyelinase-induced increase in 2-Deoxyglucose uptake could not be reproduced by preincubating the muscles with 50 microM phosphorylcholine, 50 microM C2-ceramide or 50 microM C6-ceramide. Preincubation of muscles with 50 microM sphingosine augmented basal 2-Deoxyglucose transport by 32%, but reduced the response to 0.1 and 1.0 m-unit of insulin/ml by 17 and 27% respectively. The stimulatory effect of sphingomyelinase on basal and insulin-induced 2-Deoxyglucose uptake was not influenced by either removal of Ca2+ from the incubation medium or dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum. This demonstrates that Ca2+ does not mediate the action of sphingomyelinase on 2-Deoxyglucose uptake. Sphingomyelinase also had no effect on basal and insulin-stimulated activities of insulin receptor tyrosine kinase and phosphatidylinositol 3-kinase. In addition, 1 and 5 microM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, failed to inhibit the sphingomyelinase-induced increase in 2-Deoxyglucose uptake. These results suggest that sphingomyelinase does not increase 2-Deoxyglucose uptake by stimulating the insulin receptor or the initial steps of the insulin-transduction pathway. The data suggest the possibility that sphingomyelinase increases basal and insulin-stimulated 2-Deoxyglucose uptake in skeletal muscle as the result of an unknown post-receptor effect.
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Insulin-Stimulated Phosphatidylinositol 3-Kinase Activity and 2-Deoxy-D-Glucose Uptake in Rat Skeletal Muscles
Biochemical and Biophysical Research Communications, 1995Co-Authors: Jeffrey S Elmendorf, Alice Damrau-abney, T. R. Smith, T.s. David, Jiri TurinskyAbstract:Abstract To date there is suggestive evidence that phosphatidylinositol 3-kinase participates in insulin-stimulated glucose transport. However, its involvement in skeletal muscle, a major site of insulin-stimulated glucose disposal, has not been addressed. Therefore, we tested the effects of wortmannin, a known inhibitor of phosphatidylinositol 3-kinase, on insulin-stimulated 2-Deoxyglucose uptake by rat soleus muscle in vitro. Wortmannin (1 μM) reversibly inhibited insulin-induced 2-Deoxyglucose uptake in soleus muscle by 44%. Inclusion of 5 μM wortmannin in the incubation medium completely abolished the insulin-induced increment in 2-Deoxyglucose uptake. In conclusion, the results are consistent with the concept that phosphatidylinositol 3-kinase plays a role in the insulin-signaling cascade linking insulin-receptor tyrosine kinase activation to glucose uptake in skeletal muscle.
Alice Damrau-abney - One of the best experts on this subject based on the ideXlab platform.
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Effect of monensin on 2-Deoxyglucose uptake, the insulin receptor and phosphatidylinositol 3-kinase activity in rat muscle.
The Journal of endocrinology, 1997Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, Terry R. SmithAbstract: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.
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Sphingomyelinase stimulates 2-Deoxyglucose uptake by skeletal muscle.
The Biochemical journal, 1996Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, G W Nagel, T. R. SmithAbstract:The effects of sphingomyelinase, phosphorylcholine, N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide) and sphingosine on basal and insulin-stimulated cellular accumulation of 2-deoxy-D-glucose in rat soleus muscles were investigated. Preincubation of muscles with sphingomyelinase (100 or 200 m-units/ml) for 1 or 2 h augmented basal 2-Deoxyglucose uptake by 29-91%, and that at 0.1 and 1.0 m-unit of insulin/ml 32-82% and 19-25% respectively compared with control muscles studied at the same insulin concentrations. The sphingomyelinase-induced increase in basal and insulin-stimulated 2-Deoxyglucose uptake was inhibited by 91% by 70 microM cytochalasin B, suggesting that it involves glucose transporters. Sphingomyelinase had no effect on the cellular accumulation of L-glucose, which is not transported by glucose transporters. The sphingomyelinase-induced increase in 2-Deoxyglucose uptake could not be reproduced by preincubating the muscles with 50 microM phosphorylcholine, 50 microM C2-ceramide or 50 microM C6-ceramide. Preincubation of muscles with 50 microM sphingosine augmented basal 2-Deoxyglucose transport by 32%, but reduced the response to 0.1 and 1.0 m-unit of insulin/ml by 17 and 27% respectively. The stimulatory effect of sphingomyelinase on basal and insulin-induced 2-Deoxyglucose uptake was not influenced by either removal of Ca2+ from the incubation medium or dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum. This demonstrates that Ca2+ does not mediate the action of sphingomyelinase on 2-Deoxyglucose uptake. Sphingomyelinase also had no effect on basal and insulin-stimulated activities of insulin receptor tyrosine kinase and phosphatidylinositol 3-kinase. In addition, 1 and 5 microM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, failed to inhibit the sphingomyelinase-induced increase in 2-Deoxyglucose uptake. These results suggest that sphingomyelinase does not increase 2-Deoxyglucose uptake by stimulating the insulin receptor or the initial steps of the insulin-transduction pathway. The data suggest the possibility that sphingomyelinase increases basal and insulin-stimulated 2-Deoxyglucose uptake in skeletal muscle as the result of an unknown post-receptor effect.
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Insulin-Stimulated Phosphatidylinositol 3-Kinase Activity and 2-Deoxy-D-Glucose Uptake in Rat Skeletal Muscles
Biochemical and Biophysical Research Communications, 1995Co-Authors: Jeffrey S Elmendorf, Alice Damrau-abney, T. R. Smith, T.s. David, Jiri TurinskyAbstract:Abstract To date there is suggestive evidence that phosphatidylinositol 3-kinase participates in insulin-stimulated glucose transport. However, its involvement in skeletal muscle, a major site of insulin-stimulated glucose disposal, has not been addressed. Therefore, we tested the effects of wortmannin, a known inhibitor of phosphatidylinositol 3-kinase, on insulin-stimulated 2-Deoxyglucose uptake by rat soleus muscle in vitro. Wortmannin (1 μM) reversibly inhibited insulin-induced 2-Deoxyglucose uptake in soleus muscle by 44%. Inclusion of 5 μM wortmannin in the incubation medium completely abolished the insulin-induced increment in 2-Deoxyglucose uptake. In conclusion, the results are consistent with the concept that phosphatidylinositol 3-kinase plays a role in the insulin-signaling cascade linking insulin-receptor tyrosine kinase activation to glucose uptake in skeletal muscle.
T. R. Smith - One of the best experts on this subject based on the ideXlab platform.
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Sphingomyelinase stimulates 2-Deoxyglucose uptake by skeletal muscle.
The Biochemical journal, 1996Co-Authors: Jiri Turinsky, Alice Damrau-abney, Jeffrey S Elmendorf, G W Nagel, T. R. SmithAbstract:The effects of sphingomyelinase, phosphorylcholine, N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide) and sphingosine on basal and insulin-stimulated cellular accumulation of 2-deoxy-D-glucose in rat soleus muscles were investigated. Preincubation of muscles with sphingomyelinase (100 or 200 m-units/ml) for 1 or 2 h augmented basal 2-Deoxyglucose uptake by 29-91%, and that at 0.1 and 1.0 m-unit of insulin/ml 32-82% and 19-25% respectively compared with control muscles studied at the same insulin concentrations. The sphingomyelinase-induced increase in basal and insulin-stimulated 2-Deoxyglucose uptake was inhibited by 91% by 70 microM cytochalasin B, suggesting that it involves glucose transporters. Sphingomyelinase had no effect on the cellular accumulation of L-glucose, which is not transported by glucose transporters. The sphingomyelinase-induced increase in 2-Deoxyglucose uptake could not be reproduced by preincubating the muscles with 50 microM phosphorylcholine, 50 microM C2-ceramide or 50 microM C6-ceramide. Preincubation of muscles with 50 microM sphingosine augmented basal 2-Deoxyglucose transport by 32%, but reduced the response to 0.1 and 1.0 m-unit of insulin/ml by 17 and 27% respectively. The stimulatory effect of sphingomyelinase on basal and insulin-induced 2-Deoxyglucose uptake was not influenced by either removal of Ca2+ from the incubation medium or dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum. This demonstrates that Ca2+ does not mediate the action of sphingomyelinase on 2-Deoxyglucose uptake. Sphingomyelinase also had no effect on basal and insulin-stimulated activities of insulin receptor tyrosine kinase and phosphatidylinositol 3-kinase. In addition, 1 and 5 microM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, failed to inhibit the sphingomyelinase-induced increase in 2-Deoxyglucose uptake. These results suggest that sphingomyelinase does not increase 2-Deoxyglucose uptake by stimulating the insulin receptor or the initial steps of the insulin-transduction pathway. The data suggest the possibility that sphingomyelinase increases basal and insulin-stimulated 2-Deoxyglucose uptake in skeletal muscle as the result of an unknown post-receptor effect.
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Insulin-Stimulated Phosphatidylinositol 3-Kinase Activity and 2-Deoxy-D-Glucose Uptake in Rat Skeletal Muscles
Biochemical and Biophysical Research Communications, 1995Co-Authors: Jeffrey S Elmendorf, Alice Damrau-abney, T. R. Smith, T.s. David, Jiri TurinskyAbstract:Abstract To date there is suggestive evidence that phosphatidylinositol 3-kinase participates in insulin-stimulated glucose transport. However, its involvement in skeletal muscle, a major site of insulin-stimulated glucose disposal, has not been addressed. Therefore, we tested the effects of wortmannin, a known inhibitor of phosphatidylinositol 3-kinase, on insulin-stimulated 2-Deoxyglucose uptake by rat soleus muscle in vitro. Wortmannin (1 μM) reversibly inhibited insulin-induced 2-Deoxyglucose uptake in soleus muscle by 44%. Inclusion of 5 μM wortmannin in the incubation medium completely abolished the insulin-induced increment in 2-Deoxyglucose uptake. In conclusion, the results are consistent with the concept that phosphatidylinositol 3-kinase plays a role in the insulin-signaling cascade linking insulin-receptor tyrosine kinase activation to glucose uptake in skeletal muscle.
