Swelling-Activated Cl- Current in Isolated Rabbit Articular Chondrocytes: Inhibition by Arachidonic Acid

Articular chondrocytes play an important role in maintaining the structure and function of the cartilage in synovial joints, which is closely influenced by mechanical or osmotic stress. In the present Study, isolated rabbit articular chondrocytes were examined during hyposmotic stress using the whole-cell patch-clamp method. When exposed to hyposmotic external solutions (approximately 5% or 32% decrease in osmolarity), isolated rabbit articular chondrocytes exhibited hyposmotic cell swelling, accompanied by the activation of the swelling-activated Cl- current (I-Cl,I-swell). I-Cl,I-swell was practically time-independent at potentials negative to +50 mV but exhibited rapid inactivation at more positive potentials. I-Cl,I-swell was potently inhibited by the Cl- channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid, glibenclamide, and tamoxifen, but was little affected by pimozide. I-Cl,I-swell was also found to be acutely inhibited by arachidonic acid in a concentration-dependent manner with an IC50 of 0.81 mu M. The maximal effect (approximately 100% block) was obtained with 10 mu M arachidonic acid. The arachidonic acid metabolites prostaglandin E-2, leukotriene B-4, and leukotriene D-4 had no appreciable effect on I-Cl,I-swell, suggesting that the inhibitory effect of arachidonic acid did not require its metabolism. The present study thus reveals the presence of I-Cl,I-swell in rabbit articular chondrocytes that exhibits high sensitivity to direct inhibition by arachidonic acid.