DECREASED SKELETAL-MUSCLE PHOSPHOTYROSINE PHOSPHATASE (PTPASE) ACTIVITY TOWARDS INSULIN-RECEPTORS IN INSULIN-RESISTANT ZUCKER RATS MEASUREDBY DELAYED EUROPIUM FLUORESCENCE

In order to measure the phosphotyrosine phosphatase (PTPase) activity in small muscle biopsies, a sandwich-immunofluorescence assay was deve loped using the phosphorylated human insulin receptor as a substrate, a C-terminal insulin receptor antibody as catching antibody and Europi um-labelled anti-phosphotyrosine as detecting antibody, Soluble and pa rticulate muscle fractions were prepared from soleus muscle of obese, diabetic (fa/fa) Zucker rats and their lean littermates (Fa/-). In the soluble muscle fractions of the obese (fa/fa) rats PTPase activity wa s significantly reduced compared to control (Fa/-) rats (45.2+/-2.6% v s 61.3+/-4.7%, p < 0.02). This reduction was completely prevented by 2 4 days of metformin treatment which decreased plasma glucose and plasm a insulin levels, In particulate muscle fractions, however, no differe nce in PTPase activity was found among any groups of rats examined, Th ese results show that the alterations in soluble PTPase activity in th e insulin-resistant, diabetic Zucker rat vary with the abnormality in glucose homeostasis.