Figure 6.

(a and b) Tyrosine phosphorylation and protein levels of IRβ in the aorta and liver after euglycemic hyperinsulinemic clamp. Animals were infused with saline (control) or insulin (10 mU/kg/min) for 1 hour during a euglycemic clamp as described in Methods. The aorta and liver were removed, and equal amounts of protein were subjected to immunoprecipitation with IRβ antibody, separated by SDS-PAGE, and immunoblotted with αPY antibody (top panels). Stripped membranes were reblotted with αIRβ antibody (middle panels). Data (mean ± SD; n = 4) are expressed as relative to control, assigning a value of 100% to the lean control mean. *P < 0.05, insulin lean vs. insulin obese. (c) Hybrid IR/IGF-1R in microvessels of lean and obese rats. Isolated microvessels were homogenized, and lysates (6 mg protein) were subjected to immunoprecipitation with αIRβ or IGF-1Rβ antibodies, separated by SDS-PAGE, and immunoblotted with αIGF-1Rβ or αIRβ antibodies as indicated. Stripped membranes were reblotted with αIRβ antibody (middle). The percentage of hybrid receptors in total IR was calculated by the ratio between PhosphorImager counting of IGF-1Rβ bands (top) and IRβ bands (middle) in αIRβ immunoprecipitates. *P < 0.05, lean vs. obese rats (n = 3; each sample of microvessels was derived from 2 rats).