For more than 30 yr, adipocytes have been an almost ideal model for the study of insulin action, because they can be prepared easily as a homogenous population of cells, they exhibit a marked hormonal response, and they can be fractionated into relatively pure membrane preparations. This subcellular fractionation has provided the breakthrough finding that insulin stimulates a translocation of glucose transporters (GLUTs) from an intracellular pool into the plasma membrane (1 ). A second model for the study of adipose tissue (AT) metabolism is the 3T3-L1 cell line, which differentiates to an adipocyte-like phenotype. In these cultured cells, long-term effects of hormones and agents can be investigated. As in fat cells, the effects of insulin on the subcellular distribution of GLUTs can be demonstrated in 3T3-L1 cells after fractionation (2 ). In addition, 3T3-L1 cells allow the preparation of membrane sheets still adhering to the culture dish, e.g., for immunofluorescence (3 ).
