Divergent molecular mechanisms for insulin-resistant glucose transport in muscle and adipose cells in vivo.

Glucose homeostasis depends on regulated changes in glucose transport in insulin-responsive tissues (e.g. muscle and adipose cells). This transport is mediated by at least two distinct glucose transporters: "adipose-muscle" and "erythrocyte-brain." To understand the molecular basis for in vivo insulin resistance we investigated the effects of fasting and refeeding on the expression of these two glucose transporters in adipose cells and skeletal muscle. In vivo insulin resistance seen with fasting and hyperresponsiveness seen with refeeding influence glucose transporter expression in a transporter-specific and tissue-specific manner. In adipose cells only the adipose-muscle glucose transporter mRNA and protein decrease dramatically with fasting and increase above control levels with refeeding, changes that parallel effects on insulin-stimulated glucose transport. In contrast, in muscle expression of both glucose transporters increase with fasting and return to control levels with refeeding, also in accordance with changes in glucose uptake in vitro. Although expression of the adipose-muscle glucose transporter predicts the physiological response at the tissue level, factors in the hormonal/metabolic milieu appear to override its increased expression in muscle resulting in insulin-resistant glucose uptake in this tissue in vivo.