Figure 4.

Intracellular PTP activity assay. NIH-3T3-IR cells (7.5 × 10⁵) were serum starved for 24 h before being treated with 30 ng/ml platelet-derived growth factor, 10 nM insulin, or 30 ng/ml platelet-derived growth factor together with 10 nM insulin for the indicated times. Cells were lysed in 0.1 M sodium acetate buffer, pH 5.5, and sonicated for 10 s and then were assayed for PTP activity by using either pNPP (A) or [pTyr¹¹⁴⁶]-insulin receptor fragment 1142–1153 (B). All experiments were performed in triplicate.