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

摘要

To investigate how Ca²⁺ regulates airway ciliary activity, changes in ciliary beat frequency (CBF) and intracellular calcium concentration ([Ca²⁺]i) of rabbit tracheal ciliated cells, in response to ATP, were simultaneously quantified with high-speed phase-contrast and fast fluorescence imaging. [ATP]≤ 1 μm induced an increase in[Ca²⁺]i and CBF that declined to the initial basal levels and was followed by irregular brief increases in[Ca²⁺]i and CBF. [ATP] > 1 but < 16 μm induced a similar increase in[Ca²⁺]i and CBF but this was followed by oscillations in CBF and[Ca²⁺]i. The minimum CBF of the oscillations in CBF remained elevated above the basal rate while the minimum concentration of the[Ca²⁺]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[Ca²⁺]i were induced by ATP- γ -S. Although ADP, AMP and adenosine induced a Ca²⁺-independent increase in CBF, neither ATP nor ATP- γ -S induced an increase in CBF when the Ca²⁺ increases were abolished by 20 μm BAPTA AM, a result suggesting that ATP hydrolysis was minimal. [ATP] ≥16 μm induced a sustained elevation in CBF and only a temporary, non-oscillating increase in[Ca²⁺]i. A similar response was induced by thapsigargin (2 μm). Flash photolysis of caged Ca²⁺ (NP-EGTA) produced both transient and prolonged increases in[Ca²⁺]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 Ca²⁺ -dependent mechanism that generates the rapid increases in CBF associated with the oscillations or by an indirect Ca²⁺-dependent mechanism that is responsible for the sustained minimum increase in CBF.