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 (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.


CONCLUSIONS
These results indicate that hypo-osmotic stress induces a gelsolin-mediated reorganization of actin through a transient increase in [Ca(2+)](i).
Erickson
G R
GR
Orthopaedic Research Laboratories, Department of Surgery, Duke University Medical Center, 27710, Durham,NC, USA
Northrup
D L
DL
Guilak
F
F
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D002358:Cartilage, Articular / Q000378:metabolism*; D019902:Chondrocytes / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D018260:Gelsolin / Q000378:metabolism; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D008164:Luminescent Proteins; D018613:Microscopy, Confocal; D009995:Osmosis / Q000502:physiology; D013552:Swine
D000199:Actins; D018260:Gelsolin; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium