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Hypo-osmotic stress induces calcium-dependent actin reorganization in articular chondrocytes
G R Erickson1, D L Northrup, F Guilak
1Orthopaedic Research Laboratories, Department of Surgery, Duke University Medical Center, 27710, Durham,NC, USA
Objective:
The aim of this study was to investigate the effects of hypo-osmotically induced calcium (Ca(2+)) 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 [Ca(2+)](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 [Ca(2+)](i)caused reorganization of intracellular actin through a mechanism that required Ca(2+)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 [Ca(2+)](i).