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Polymyxin B selectively inhibits insulin effects on transport in isolated muscle
Abstract:
Polymyxin B (PMB), a cyclic decapeptide antibiotic, inhibits the hypoglycemic effect of insulin in vivo. To elucidate the mechanism of PMB action, we have studied its effect in vitro on insulin-stimulated pathways in the mouse skeletal muscle. PMB, added to the incubation mixture, specifically inhibited insulin-stimulated 2-deoxyglucose transport and alpha-aminoisobutyric acid uptake in the isolated soleus muscle but did not affect the basal rates of transport (measured in the absence of insulin). PMB did not alter insulin binding and hexokinase activity. PMB effect was observed at all deoxyglucose concentrations tested, and PMB was also able to inhibit vanadate-stimulated glucose transport. By contrast, insulin activation of glycogen synthase was not prevented by PMB. Basal and maximally insulin-stimulated insulin receptor tyrosine kinase activity, tested in a cell-free system, was similar for both autophosphorylation and phosphorylation of exogenous substrates in the absence or in the presence of PMB. Furthermore, the insulin sensitivity of the kinase was increased in the presence of PMB. Our results suggest that the anti-insulin effect of PMB observed in vivo is due to an inhibition of insulin-stimulated glucose transport in the skeletal muscle perhaps through a specific blockade of the insulin-induced translocation of the glucose carriers.
Insights
Polymyxin B (PMB) inhibits insulin-stimulated glucose transport in mouse skeletal muscle, potentially by blocking glucose carrier translocation. This antibiotic
Area of Science:
- Biochemistry
- Pharmacology
- Cell Biology
Background:
- Polymyxin B (PMB) is a cyclic decapeptide antibiotic known to inhibit insulin's hypoglycemic effect in vivo.
- The precise mechanism underlying PMB's anti-insulin activity remains unclear.
Purpose of the Study:
- To investigate the in vitro mechanism by which Polymyxin B interferes with insulin-stimulated pathways in mouse skeletal muscle.
- To determine if PMB affects glucose transport, insulin binding, or receptor kinase activity.
Main Methods:
- Isolated mouse soleus muscles were used to assess insulin-stimulated 2-deoxyglucose and alpha-aminoisobutyric acid uptake.
- Insulin binding assays, hexokinase activity measurements, and insulin receptor tyrosine kinase activity assays were performed.
- Vanadate-stimulated glucose transport was also evaluated.
Main Results:
- Polymyxin B specifically inhibited insulin-stimulated glucose and amino acid transport but not basal transport rates.
- PMB did not affect insulin binding or hexokinase activity.
- PMB inhibited vanadate-stimulated glucose transport and did not prevent insulin activation of glycogen synthase or insulin receptor tyrosine kinase activity.
Conclusions:
- The anti-insulin effect of Polymyxin B in vivo likely stems from its inhibition of insulin-stimulated glucose transport in skeletal muscle.
- PMB may act by specifically blocking the translocation of glucose carriers induced by insulin.