Ca2+-sensitive phosphoinositde hydrolysis is activated in synovial cells but not in articular chondrocytes
| Autor: | Paola D'Andrea, Ilaria Capozzi, Rossana Tonon |
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| Přispěvatelé: | Capozzi, I., Tonon, R., D'Andrea, Paola |
| Rok vydání: | 1999 |
| Předmět: |
Cartilage
Articular Connexin Biology Phosphatidylinositols Biochemistry Connexins chemistry.chemical_compound Adenosine Triphosphate Chondrocytes Cytosol Physical Stimulation Extracellular Animals Inositol Calcium Signaling Inositol phosphate Molecular Biology chemistry.chemical_classification Hydrolysis Ionomycin Synovial Membrane Gap junction Cell Biology chemistry Connexin 43 Type C Phospholipases Second messenger system Biophysics Rabbits Intracellular Research Article |
| Popis: | Cell-to-cell diffusion of second messengers across intercellular channels allows tissues to co-ordinate responses to extracellular stimuli. Intercellular diffusion of inositol 1,4,5-trisphosphate, locally produced by focal stimulations, sustains the propagation of intercellular Ca(2+) waves, by stimulating the release of intracellular Ca(2+) in neighbouring cells. We previously demonstrated that in cultured articular chondrocytes and HIG-82 synovial cells, studied with digitial fluorescence video imaging, mechanical stimulation of a single cell induced intercellular Ca(2+) waves dependent on the presence of gap junctions. In the absence of extracellular Ca(2+) the propagating distance of the wave decreased significantly in HIG-82 cells, but appeared unaffected in chondrocytes. We now show that both cells types express connexin 43 and a similar functional coupling, thus suggesting that the different Ca(2+) sensitivity of intercellular waves is not due to major differences in gap junction constituent proteins. In HIG-82 synoviocytes, but not in chondrocytes, the Ca(2+) ionophore ionomycin stimulated phosphoinositide hydrolysis in a concentration-dependent manner, an effect strictly dependent on the presence of extracellular Ca(2+), suggesting the expression, in these cells, of a Ca(2+)-sensitive phospholipase C activity. Such an activity could be stimulated also by Ca(2+) influx induced by P(2Y) receptor activation and considerably amplifies ATP-induced inositol phosphate (InsP) production. In contrast, Ca(2+) influx did not affect considerably the response of chondrocytes to ATP stimulation. In HIG-82 cells, the combined application of ionomycin and ATP maximally stimulated InsP synthesis, suggesting the involvement of two independent mechanisms in inositol phosphate generation. These results suggest that in HIG-82 synovial cells the recruitment of a Ca(2+)-sensitive phospholipase C activity could amplify the cell response to a focally applied extracellular stimulus, thus providing a positive feedback mechanism for intercellular wave propagation. |
| Databáze: | OpenAIRE |
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