Oscillations in ciliary beat frequency and intracellular calcium concentration in rabbit tracheal epithelial cells induced by ATP

To investigate how Ca 2+ regulates airway ciliary activity, changes in ciliary beat frequency (CBF) and intracellular calcium concentration ([Ca 2+ ] i ) of rabbit tracheal ciliated cells, in response to ATP, were simultaneously quantified with high‐speed phase‐contrast and fast fluorescence imaging. [ATP]⩽ 1 μ m induced an increase in [Ca 2+ ] i and CBF that declined to the initial basal levels and was followed by irregular brief increases in [Ca 2+ ] i and CBF. [ATP] > 1 but < 16 μ m induced a similar increase in [Ca 2+ ] i and CBF but this was followed by oscillations in CBF and [Ca 2+ ] i . The minimum CBF of the oscillations in CBF remained elevated above the basal rate while the minimum concentration of the [Ca 2+ ] i oscillations returned to the basal level. The minimum and maximum CBF of the oscillations in CBF were independent of the [ATP], whereas the frequency of the oscillations in CBF was dependent on the [ATP]. Similar oscillations in CBF and [Ca 2+ ] i were induced by ATP‐ γ ‐S. Although ADP, AMP and adenosine induced a Ca 2+ ‐independent increase in CBF, neither ATP nor ATP‐ γ ‐S induced an increase in CBF when the Ca 2+ increases were abolished by 20 μ m BAPTA AM, a result suggesting that ATP hydrolysis was minimal. [ATP]≥16 μ m induced a sustained elevation in CBF and only a temporary, non‐oscillating increase in [Ca 2+ ] i . A similar response was induced by thapsigargin (2 μ m ). Flash photolysis of caged Ca 2+ (NP‐EGTA) produced both transient and prolonged increases in [Ca 2+ ] i which were accompanied by transient and sustained increases in CBF, respectively. From these results, we propose that CBF can be increased by a direct Ca 2+ ‐dependent mechanism that generates the rapid increases in CBF associated with the oscillations or by an indirect Ca 2+ ‐dependent mechanism that is responsible for the sustained minimum increase in CBF.