Regulation of Airway Ciliary Activity by Ca2+: Simultaneous Measurement of Beat Frequency and Intracellular Ca2+

Abstract

Airway ciliary activity is influenced by [Ca2+]i, but this mechanism is not fully understood. To investigate this relationship, ciliary activity and [Ca2+]i were measured simultaneously from airway epithelial ciliated cells. Ciliary beat frequency was determined, for each beat cycle, with phase-contrast optics and high-speed video imaging (at 240 images s−1) and correlated with [Ca2+]i determined, at the ciliary base, by fast imaging (30 images s−1) of fura-2 fluorescence. As a mechanically induced intercellular Ca2+ wave propagated through adjacent cells, [Ca2+]i was elevated from a baseline concentration of 45 to 100 nM, to a peak level of up to 650 nM. When the Ca2+ wave reached the ciliary base, the beat frequency rapidly increased, within a few beat cycles, from a basal rate of 6.4 to 11.6Hz at 20–23°C, and from 17.2 to 26.7Hz at 37°C. Changes in [Ca2+]i, above 350 nM, had no effect on the maximum beat frequency. We suggest that airway ciliary beat frequency is 1) controlled by a low range of [Ca2+]i acting directly at an axonemal site at the ciliary base and 2) that a maximum frequency is induced by a change in [Ca2+]i of ∼250–300 nM.