Abstract: AIM: To investigate the effects of various extracellular solutions on rat chondrocytes proliferation and apoptosis in vitro, and relation of Cathepsin K mRNA expression and extracellular acidosis.METHODS: Articular chondrocytes were obtained from rats using type II collagenase digestion method. The chondrocytes were divided into four groups and incubated in different pH extracelluar solution (pH 7.4, pH6.5, pH6.0, pH5.5) for three hours. MTT assay was employed to determine the proliferation of articular chondrocytes in acidic solutions. Effects of extracellular acidosis on chondrocyte apoptosis were observed by Hoechst 33258 and Annexin V/PI staining. The expression of Cathepsin K mRNA were detected by real time reverse transcription PCR.RESULTS: Proliferation of articular chondrocytes were inhibited observably by acidosis (P<0.05). Apoptosis rate of articular chondrocytes were increased comparing with control group (P<0.05). The expression of Cathepsin K mRNA level gradually increased following the degree of acidity in extracellular solution.CONCLUSION: Extracellular acidosis can restrain the proliferation and promote the apoptosis of articular chondrocytes in vitro, and increase the expression of Cathepsin K mRNA. It has provided an experimental evidence on mechanism bone destruction in Rheumatoid arthritis.

Key words: Extracellular acidification, Apoptosis, Rheumatoid arthritis, Chondrocytes