The failure of insulin-regulated recruitment of the GLUT4 glucose transporter in cardiac muscle of obese Zucker rats is associated with alterations of the subcellular distribution of the small-molecular-mass GTP-binding protein rab4A. Here, we show by subcellular fractionation and Western blotting a translocation of the small-molecular-mass GTP-binding protein rab3C from microsomal membranes to plasma membranes in lean control rats following in vivo insulin stimulation. However, in cardiac muscle of obese animals no significant effect of the hormone on the subcellular distribution of rab3C was observed. In GLUT4-enriched membrane vesicles, obtained from cardiac microsomes of the obese group as well as of lean controls, rab3C was not detectable. It is suggested that the altered behaviour of rab3C may contribute to an impaired trafficking of GLUT4 in the insulin-resistant state.
