Epithelial cilia

Drug deposited on the mucous lining of the bronchial epithelium is partly absorbed and partly transported with bronchial mucus towards the larynx. Bronchial mucus travels upwards due to the orally directed undulatory beat of the epithelial cilia. Physiologically, this Lullmann, Color Atlas of Pharmacology... 

Components of coltsfoot have also been noted to increase the activity of epithelial cilia in the frog esophagus, possibly giving credence to use of coltsfoot as an expectorant (Anonymous, 1996). 

Experimental systems in animals can provide valuable insights into the cellular and molecular mechanisms of disease. Despite considerable efforts, there are still no good animal models of COPD. However, the use of chemical and irritant-induced injury models, combined with more mechanistic studies have provided some useful insights into a variety of disease relevant processes and may represent useful alternatives. Airway exposure to agents such as tobacco smoke (32,33), sulfur dioxide (34), cadmium chloride (35), and EPS (36) induce lung injury characterized by increases in neutrophils and macrophages within the central and peripheral airways, a loss of epithelial cilia through the upper airways. 

A typical cross section of a cilium shows a ring formed by nine pairs of microtubules and two central tubules, i.e., the so-called nine + two pattern. Each doublet contains an A and a B subfibril with an inner and an outer dynein arm (a complex protein with ATPase activity) located on the A subfibril with radial spokes extending toward the central doublet. The ciliary membrane, which is an extension from the cell membrane of the epithelial cell, encloses the microtubules. The motion of the cilia is dependent on the sliding of the outer doublets past one another with the energy provided by adenosine triphosphate (ATP) through dynein ATPase activity. 

The olfactory epithelium is composed of basal, neuronal (olfactory), and susten-tacular (support) cells (Figure 27.3). The portion of each olfactory cell that responds to the olfactory chemical stimuli is the cilia. The odorant substance first diffuses into the mucus that covers the cilia and then binds to specific receptor proteins in the membrane of each cilium. Next, receptor activation by the odorant activates a multiple molecules of the G-protein complex in the olfactory epithelial cell. This, in turn, activates adenylyl cyclase inside the olfactory cell membrane, which, in turn, causes formation of a greater multitude of cAMP molecules. Finally, the cAMP molecules trigger the opening of yet an even greater multitude of sodium ion channels. This amplification mechanism accounts for the exquisite sensitivity of the olfactory neurons to extremely small amounts of odorant. The olfactory epithelium is an important target of certain inhaled toxicants. Certain metals, solvents, proteins, and viruses are transported to the brain via transport from the olfactory epithelium to the olfactory tract and exert neurotoxicity. 

Radford R et al (2012) Carcinogens induce loss of the primary cilium in human renal proximal tubular epithelial cells independently of effects on the cell cycle. Am J Physiol Renal Physiol 302(8) F905-F916... 

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