Abstract
Articular chondrocytes play a crucial role in the production and maintenance of extracellular matrix, which is influenced by mechanical and osmotic environment. The present study investigated the mechanisms underlying activation of ICl,vol in rabbit chondrocytes using whole-cell patch-clamp method. Exposure of chondrocytes to the hyposmotic solution resulted in a cell swelling, which was accompanied by the activation of ICl,vol. Bath application of tyrosine kinase inhibitor genistein partially and reversibly blocked ICl,vol but its inactive analogue daidzein had little effect. On the other hand, intracellular application of tyrosine phosphatase inhibitor orthovanadate via a recording pipette gradually activated an outwardly rectifying current with a reversal potential of -20.3 mV close to the predicted Cl− equilibrium potential of -18.3 mV even under isosmotic condition. This orthovanadate-evoked current was almost completely abolished by the Cl− channel blocker DIDS and was also largely reduced by cell shrinkage caused by exposure to hyperosmotic solution. Pretreatment of chondrocytes with genistein significantly prevented the activation of Cl− current by orthovanadate, suggesting that the basal activity of tyrosine kinase is required for the orthovanadate-evoked activation of Cl− current. Our results strongly suggest that tyrosine phosphorylation is involved in the activation process of ICl,vol in rabbit articular chondrocytes. [J Physiol Sci. 2008;58 Suppl:S81]
