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

Abstract

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 inducedan 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.