Expression of pERK1/2 in differentiated primary calvarial osteoblasts isolated from the WT and the pd mice. Differentiated calvarial osteoblasts were treated with 100 nM PTHrP (Pr), PTH (P), or vehicle (V) for 10 min. Total cellular protein was harvested. Western blot analyses were performed for total ERK1/2 and phosphorylated ERK1/2. Densitometric analyses were performed, normalized to total ERK1/2, and plotted. Representative data from at least three to four independent experiments are shown. Data are expressed as mean±S.D. c, P<0.05 versus V. pd, phosphorylation-deficient PTH1R; WT, wild-type.