p38 and JNK MAPK pathways regulate OCP crystal induced NO production and iNOS mRNA expression. Nonadherent bovine articular chondrocytes were stimulated with OCP crystals or IL-1β for 24 hours with or without pretreatment (1 hour) with (a,c) SB 203580 (a p38 MAPK inhibitor), (b,c) JNK II inhibitor or (d) PD 58059 (an Erk1/2 MAPK inhibitor). iNOS transcripts (panel d) were assessed 8 hours after stimulation by OCP crystals or IL-1β by RT-PCR. The RT-PCR was representative of three experiments. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; iNOS, inducible nitric oxide synthase; JNK, c-Jun amino-terminal kinase; NO, nitric oxide; OCP, octacalcium phosphate.