Insulin-like growth factor (IGF)-1 receptor (IGF-1R) levels and activation in normal and osteoarthitis (OA) osteoblasts. Cells were grown to confluence and incubated overnight in serum free medium. (a) After cell lysis in RIPA buffer and immunoprecipitation with an anti-IGF-1R α-subunit antibody (ab 4), receptor levels were analyzed by western immunoblot with an anti-IGF-1R α-subunit antibody (ab 5). (b) After cell lysis in RIPA buffer, tyrosine phosphorylation of the receptor exposed to 50 ng/ml IGF-1 for 5 minutes was analyzed with anti-IGF-1R phosphotyrosine ab (PY-1158). Determination of actin was used as the control for loading. Representative data are shown in panel 1 (a,b). Results expressed as arbitrary scanning units are presented as the mean ± SEM (panel 2 (a,b)).