Immune localization of calmodulin in the ciliated cells of hamster tracheal epithelium.

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Abstract
Metachronal beating of cilia of epithelial surfaces of most respiratory airways moves the overlying mucous layer in a caudal direction. The molecular mechanisms controlling ciliary beat remain largely unknown. Ca, an element in its cationic form, is ubiquitous in biological functions and its concentration is critical for ciliary beating. Calmodulin, a Ca-binding protein which regulates the activity of many enzymes and cellular processes, may regulate ciliary beating by controlling enzymes responsible for mechanochemical movement between adjacent peripheral microtubule doublets composing the ciliary axoneme. As a 1st step in describing a calmodulin-related controlling mechanism for ciliary beating, calmodulin was localized in the ciliated cells lining the respiratory tracts of hamsters by EM using an indirect immunoperoxidase technique with anticalmodulin antibodies as the molecular probe. Thin-sections revealed calmodulin located on microtubules and dynein arms of the ciliary shaft, basal body, apical cytoskeletal microtubules and plasma membranes in specimens fixed with 1 mM Ca2+. Specimens fixed with less Ca2+ (1 .mu.M), Mn2+, Mg2+, and EGTA showed a diffuse pattern of calmodulin with loci of greatest densities on basal body microtubule triplets. Demembranated specimens showed a less specific localization on axonemal microtubules but only on cells fixed with Ca2+. Calmodulin, by binding Ca, may function in ciliary beating in the respiratory tract of mammals either directly or indirectly through its effects on the energy-producing enzymes and by control of Ca2+ flux through plasma membranes.