OCP crystal induced p38 and JNK MAPK activation. Nonadherent bovine articular chondrocytes were stimulated with OCP crystals for 20 min with or without pretreatment (1 hour) with SB 203580 or JNK II inhibitor. Fifteen (p38 MAPK) or 30 μg (JNK MAPK) protein of cell lysates were subjected to SDS-PAGE/Western blot analysis. The blots were probed with phosphospecific (a) p38 and (b) JNK MAPK antibodies. To ensure equal loading, the blot was stripped and reprobed with total p38 MAPK or JNK antibodies. JNK, c-Jun amino-terminal kinase; OCP, octacalcium phosphate.