Nature of the mammalian ciliary metachronal wave

Abstract

The temporal and spatial coordination of ciliary beat (metachronicity) is fundamental to effective mucociliary transport. Metachronal wave period (MWP) and ciliary beat frequency (CBF) of fresh excised sheep and canine tracheal epithelial tissues were measured with the use of a newly developed alternating focal spot laser light scattering system. MWP was determined from cross correlation of the heterodyne signals from the alternating focal spots. CBF was determined by autocorrelation of the heterodyne signals from each of the spots. MWP and CBF were measured in four sheep tracheal epithelial tissues with the use of longitudinal interfocal spot distances of 6 and 18 microns. In three canine tracheal epithelial tissues MWP and CBF were measured both longitudinally and circumferentially with interfocal spot distances of 5, 15, 65, 87, and 96 microns. For the sheep tracheal epithelial tissues the mean CBF was 5.9 +/- 0.4 Hz (mean of means; range 3.6 +/- 0.5 to 9.9 +/- 1.5 Hz), whereas the mean MWPs for 6- and 18-microns interfocal spot distances were 0.50 +/- 0.1 and 0.47 +/- 0.1 s, respectively. For the canine tracheal epithelial tissues the mean CBF was 4.0 +/- 0.2 Hz (2.0 +/- 0.8 to 7.2 +/- 3.2 Hz), whereas the mean longitudinal MWP was 1.5 s and the mean circumferential MWP was 2.1 s. Geometric combination of the MWP components leads to a derived MWP of 2.6 s with a propagation direction of 54 degrees with respect to the longitudinal axis of the trachea. MWP was found to be episode modulated with 12- to 20-min intervals in the longitudinal direction, but modulation was not as apparent in the circumferential direction. These data suggest that MWP and CBF are regulated by separate intracellular, intercellular, and intraciliary mechanisms.