Spontaneous oscillation and mechanically induced calcium waves in chondrocytes

The characteristics of spontaneous calcium (Ca2+) oscillation and mechanically induced Ca2+ waves in articular chondrocytes were studied. In some, but not all, chondrocytes in sliced cartilage and primary cultures, we observed spontaneous oscillation of intracellular Ca2+ that never spread to adjacent cells. In contrast, a mechanical stimulus to a single cell by touching with a glass rod induced an increase of intracellular Ca2+ that spread to neighboring cells in a wave-like manner, even though there was no physical contact between the cells. This indicated the release of some paracrine factor from the mechanically stimulated cells. Application of ultrasonic vibration also induced an oscillation of intracellular Ca2+. The application of a uridine 5′-triphosphate (UTP), UTP, induced a transient increase in intracellular Ca2+ and the release of adenosine 5′-triphosphate (ATP) in cultured chondrocytes. A P2 receptor antagonist (suramin) and blockers of Cl− channels, niflumic acid and 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), reduced the UTP-induced ATP release. The results indicated that Cl− channels were involved in the extracellular release of ATP following mechanical or P2Y receptor stimulation. Thus, ATP stimulation of P2Y receptors elicits an increase in intracellular Ca2+, triggering further release of ATP from adjacent cells, thereby expanding the Ca2+ wave in chondrocytes. Copyright © 2005 John Wiley & Sons, Ltd.