Increases in ciliary beat frequency result in a) increases in the ciliary tip velocity, b) increases in the frequency of mucus-cilia interactions and c) enhancement of cilia recruitment by extended metachronal activity. Because each of these process serve to increase mucus transport, the regulation of beat frequency will in turn regulate mucus transport.
By understanding the mechanisms that regulate ciliary beat frequency, an insight into the regulation and dysfunction of mucus clearance in airway disease can be approached.
Increases in intracellular calcium concentration ([Ca2+]i) result in increases in ciliary beat frequency of airway cilia. This association is demonstrated in cultured ciliated epithelial cells in response to mechanical stimulation of a single cell (below). However, the mechanism by which Ca2+ induces these changes in frequency are not well understood.
Real-Time Phase-Contrast Video: Following mechanical stimulation of a single cell, the beat frequency of the cilia of the stimulated cell rapidly increase. After a short delay, the cilia of adjacent cells show similar increases in beat frequency.
Real-Time Calcium Video: When [Ca2+]i is measured with fura-2, a similar mechanical stimulus, at the arrow, initiates a Ca2+ wave that spreads through adjacent cells at a similar rate as the increases in beat frequency above. Magnification is less. Cell edges marked in white.
The Problems...
Cilia beat from 10 to 30 Hz (depending on the experimental temperature). And following mechanical stimulation, as shown in the video above, the corresponding increase in ciliary beat frequency occurs very quickly. To record these fast changes in beat frequency, a high-speed video technique has been developed.
Ca2+ Dynamics in airway epithelial
cells induced by extracellular ATP (Time -lapse recording ~ x 15)
Temporal and Spatial
Changes in [Ca2+]i
Changes in [Ca2+]i
are very often dynamic in nature and do not occur homogenously across the
cell. Frequently, [Ca2+]i increases occur as waves
or repetitive oscillation (video, right). It is therefore extremely
important to monitor ciliary beat frequency of a few cilia and [Ca2+]i
at the base of the same cilia simultaneously if a correlation between
ciliary activity and [Ca2+]i
is to be made.
