OCP crystal-induced NO release by articular cartilage fragments and isolated articular chondrocytes. Nonadherent articular bovine chondrocytes (106 cells/ml) were stimulated with OCP crystals (see Materials and method). Articular cartilage fragments were dissected and cultured as described in the Materials and method section. NO accumulation was determined with the Griess reaction. (a) Dose–response NO production by chondrocytes was determined 24 hours after stimulation with different doses of OCP crystals or IL-1β. (b) Kinetics of NO release was determined after stimulation with OCP crystals (0.5 mg/ml), IL-1β (10 ng/ml) alone or preincubated with L-NAME (2 mmol/l), a nonspecific iNOS inhibitor (n = 3 different experiments). (c) NO released by articular cartilage disks, and reported to cartilage dry weight, were measured 4 days after OCP crystals or IL-1β (10 ng/ml) stimulation (n = 3). *P < 0.001, OCP versus control, L-NAME/OCP). L-NAME, NG-nitro-L-arginine methyl ester; OCP, octacalcium phosphate; PBS, phosphate-buffered saline.