oscillations

Ca²⁺ oscillations induced by ATP
Airway epithelial cells possess purinergic receptors and may use extracellular ATP as a signaling molecule to regulate beat frequency and mucus secretion. In addition, Ca²⁺ waves in other cell types appear, in part, to be mediate by extracellular ATP.
When extracellular ATP was applied to cultures of ciliated airway epithelial cells, the cells displayed a dynamic Ca²⁺ response that can be viewed in the time-lapse video (right). The response occurs in two phases. ATP initially induces a large increase in Ca²⁺. After this initial response and as the Ca²⁺ begins to return to resting concentrations, a series of Ca²⁺ oscillations are observed. These Ca²⁺ oscillations occur repetitively in single cells (from every ~ 5 - 60 secs) and frequently appear as intracellular Ca²⁺ waves that sweep across the individual cell. However, unlike mechanically stimulated Ca²⁺ waves, these intracellular Ca²⁺ waves do not propagate to adjacent cells.		Video of ATP-induced Ca2+ oscillations in cultured airway epithelial cells

The two phases and asynchronous nature of the Ca²⁺ responses of epithelial cells to ATP is also shown in the image series and graphs above. The initial surge in Ca²⁺ is seen in the top left panel and represents the first peak of the graphs (right). As Ca²⁺ returns to basal levels, the repetitive Ca²⁺ oscillations begin as indicated by the spikes in the graphs. The '*' indicate individual cells that show oscillations. In both cases, it can be seen that adjacent cells display Ca²⁺ oscillations independently of the activity of neighboring cells.

Intercellular Ca²⁺Waves: The failure of ATP-induced Ca²⁺ oscillations to propagate suggests that the epithelial cells may have lost their ability to communicate. However, if a single cell is mechanically-stimulated (arrow: middle panel, graph: dotted line with ), after the application of ATP (graph: first dotted line) and during the display of Ca²⁺ oscillations (cells marked with ), an intercellular Ca²⁺ wave is initiated that spreads through many adjacent cells. After the passage of the wave, the cells continue to oscillate (lower panel, graph).