Hypo-osmotic stress induces calcium-dependent actin reorganization in articular chondrocytes

Objective: The aim of this study was to investigate the effects of hypo-osmotically induced calcium (Ca2+) transients on the organization of the actin cytoskeleton in articular chondrocytes. The secondary hypothesis tested was that actin restructuring following hypo-osmotic stress is mediated by gelsolin. Methods: Isolated porcine chondrocytes were exposed to hypo-osmotic stress, and [Ca2+](i) was monitored using laser scanning microscopy. Calcium transients were monitored using fluorescent ratiometric imaging. The intracellular distribution of actin was examined using fluorescent immunohistochemistry and transient transfection with the pEGFP-actin plasmid. The intracellular distribution of gelsolin was investigated using fluorescent immunohistochemistry. Results: Osmotic stress induced transient increases in [Ca2+](i) caused reorganization of intracellular actin through a mechanism that required Ca2+ in the extracellular media. Fluorescence microscopy revealed that gelsolin was colocalized with F-actin immediately following hypo-osmotic stress but dissociated over time. Conclusion: These results indicate that hypo-osmotic stress induces a gelsolin-mediated reorganization of actin through a transient increase in [Ca2+](i). (C) 2003 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved.