Stimulation of mucus secretion, ciliary activity, and transport in frog palate epithelium

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Abstract
Particle transport velocity and ciliary beat frequency, at the level of a single cell of the epithelium, were measured simultaneously. The preparation used keeps the mucociliated epithelium of the frog palate functionally intact but is thin enough for light to be transmitted. The observations confirm that there exists a resting, or unstimulated, state of the epithelium in which the cilia do not beat. It is shown that tactile stimulation (contact with a small 50- to 75-microns foreign particle or with a fine wire probe) restarts ciliary beat. If the epithelium has not been depleted of its mucus, normal ciliary beat frequency is restored, and there is particle transport at the normal velocity. Only the cilia surrounding the moving particle in a patch about 10 times larger are beating at one time. Beat frequency is highest in the center of the patch, near the particle, and tapers to zero toward the edge. Mucus has to be present for particle transport to occur. Particles impacted on a depleted epithelium are not moved. The placement of previously collected endogenous mucus onto a depleted epithelium produces full ciliary activity and normal particle transport. The moving patch of beating cilia corresponds to a plaque of mucus surrounding the particle being transported. This plaque was produced upon first impact of the particle, presumably by mucus secretion, from the epithelial region which then surrounds it. Stimulation of a quiescent nondepleted epithelium with a wire probe induces a normal ciliary beat frequency that gradually decreases to zero. Stimulation by a wire probe of a mucus-depleted epithelium produces a level of initial beat frequency much below normal. Depletion of the epithelial preparation is by an episode of "creeping" over a glass surface. Depletion of the epithelium could be demonstrated histochemically. Analysis of the data of particle velocity and beat frequency is consistent with a wave-length of 45 microns for the metachronous wave.