title: Inhibitory effects of N-ethylmaleimide on insulin- and oxidant-stimulated sugar transport and on 125I-labelled insulin binding by rat soleus muscle.
abstract: These experiments examined the effects of N-ethylmaleimide on insulin- and oxidant-stimulated sugar transport in soleus muscle in terms of the Thiol-Redox model for insulin-stimulated adipocyte sugar transport (Czech, M.P. (1976) J. Cell. Physiol. 89, 661-668). Brief exposure (1 min) to N-ethylmaleimide (0.3-10 mM) inhibited the stimulatory effect of insulin (0.1 U/ml) on D-[U-14C]xylose uptake by rat soleus muscle. N-Ethylmaleimide also inhibited the stimulatory effects of H2O2 (5 mM), diamide (0.2 mM) and vitamin K-5 (0.05 mM). This effect of N-ethylmaleimide on insulin action was paralleled by the inhibition of 125I-labelled insulin binding by the muscle. N-ethylmaleimide lowered muscle ATP; however, its effects on sugar transport and 125I-labelled insulin binding could be dissociated from its effect on ATP. Exposing muscles to insulin prior to N-ethylmaleimide did not abolish the inhibitory effect of sulphydryl blockade on insulin-stimulated sugar transport, but did reduce the effect of the inhibitor by 20-30%. Conversely, when muscles were first allowed to bind 125I-labelled insulin and then exposed to the inhibitor, there was no effect of N-ethylmaleimide on pre-bound insulin. Exposure to diamide or vitamin K-5 before N-ethylmaleimide (1 mM) attenuated the inhibitory effect of sulphydryl blockade but no protective effect was observed with H2O2. None of the oxidants protected against the inhibitory effect of 3 mM N-ethylmaleimide. It is concluded that there are two N-ethylmaleimide-sensitive sites involved in the activation of muscle sugar transport at the post-receptor level. One of these would appear to be similar to the Thiol-Redox site described in the adipocyte; the other site appears to be an essential sulphydryl group whose function does not involve oxidation to a disulphide.
mesh_terms: D000818:Animals; D001391:Azo Compounds / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D003958:Diamide / Q000494:pharmacology*; D005033:Ethylmaleimide / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007328:Insulin / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism*; D014812:Vitamin K / Q000031:analogs & derivatives* / Q000494:pharmacology; D024483:Vitamin K 3 / Q000031:analogs & derivatives*; D014994:Xylose / Q000378:metabolism*
chemical_list: D001391:Azo Compounds; D007328:Insulin; C008147:insulin, iodo-; D003958:Diamide; D014812:Vitamin K; D024483:Vitamin K 3; D014994:Xylose; D006861:Hydrogen Peroxide; D011972:Receptor, Insulin; C024534:vitamin k5; D005033:Ethylmaleimide