Abstract
Melachronous 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. Calcium, an element in its cationic form, is ubiquitous in biological functions and its concentration is critical for ciliary beating. Calmodulin, a calcium-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 first 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 electron microscopy, 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 Ca+2. Specimens fixed with less Ca+2 (1 microM), Mn+2, Mg+2, 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 Ca+2. Calmodulin, by binding calcium, 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 Ca+2 flux through plasma membranes.
Highlights
Metachronal beating of cilia of epithelial surfaces of most respiratory airways moves the overlying mucous layer in a caudal direction
We present evidence that a calmodulin or a calmodulin-like molecule observed by immunoelectron microscopy using an anticalmodulin antibody is present on ciliary plasma membranes, axonemal components, and in the apical cytoplasm in the ciliated cells of the hamster respiratory tract
The normal tissue analyzed for its morphology in longitudinal and cross sections of cilia and basal bodies is shown in Figs. 2 and 3 for comparison with tissues treated for the localization of calmodulin
Summary
Metachronal beating of cilia of epithelial surfaces of most respiratory airways moves the overlying mucous layer in a caudal direction. As a first 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 electron microscopy, using an indirect immunoperoxidase technique with anticalmodulin antibodies as the molecular probe. Calmodulin, by binding calcium, 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 Ca÷2 flux through plasma membranes. We present evidence that a calmodulin or a calmodulin-like molecule observed by immunoelectron microscopy using an anticalmodulin antibody is present on ciliary plasma membranes, axonemal components, and in the apical cytoplasm in the ciliated cells of the hamster respiratory tract
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