NITRIC-OXIDE AND G-PROTEINS MEDIATE THE RESPONSE OF BOVINE ARTICULAR CHONDROCYTES TO FLUID-INDUCED SHEAR

Mechanical loading alters the metabolism of articular cartilage, possi bly due to effects of shear stress on chondrocytes. In cultured chondr ocytes, glycosaminoglycan synthesis increases in response to fluid-ind uced shear. This study tested the hypothesis that shear stress increas es nitric oxide production in chondrocytes, and nitric oxide then infl uences glycosaminoglycan metabolism. Inhibitors of nitric oxide syntha se, G proteins, phospholipase C, potassium channels, and calcium chann els were also analyzed for effects on nitric oxide release and glycosa minoglycan synthesis. Fluid-induced shear was applied to primary high- density monolayer cultures of adult bovine articular chondrocytes usin g a cone viscometer. Nitric oxide release in chondrocytes increased in response to the duration and the magnitude of the fluid-induced shear . Shear-induced nitric oxide production was reduced in the presence of nitric oxide synthase inhibitors but was unaffected by pertussis toxi n, neomycin, tetraethyl ammonium chloride, or verapamil. The increase in glycosaminoglycan synthesis in response to shear stress was blocked by nitric oxide synthase inhibitors, pertussis toxin, and neomycin bu t not by tetraethyl ammonium chloride or verapamil. The phospholipase C inhibitor, neomycin, also decreased glycosaminoglycan synthesis in t he absence of flow-induced shear. As studied here, shear stress increa sed nitric oxide production by chondrocytes, and the shear-induced cha nge in matrix macromolecule metabolism was influenced by nitric oxide synthesis: G protein activation, and phospholipase C activation.