Carbamylcholine-induced morphological changes and spatial dynamics of [Ca2+]c in Harderian glands of guinea pigs: calcium-dependent lipid secretion and contraction of myoepithelial cells |
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Authors: | Yohichi Satoh Yoshiaki Habara Tomio Kanno Kazuyuki Ono |
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Institution: | (1) Department of Anatomy, Ashikawa Medical College, 078 Asahikawa, Japan;(2) Laboratory of Cellular Metabolism, Department of Molecular Physiology, National Institute for Physiological Sciences, 444 Okazaki, Japan;(3) Department of Physiology, Faculty of Veterinary Medicine, Hokkaido University, 060 Sapporo, Japan |
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Abstract: | To determine whether lipid-secreting cells have cytosolic Ca2+ concentration (Ca2+]c)-related secretory mechanisms, morphological changes and intracellular calcium dynamics of Harderian glands of guinea pigs stimulated by secretagogs were studied by electron microspy and Fura-2/AM digital image analysis. Control glandular cells contained large lipid vacuoles that were bordered by multi-layered membranes. Rough-surfaced endoplasmic reticulum, mitochondria, and smooth-surfaced endoplasmic reticulum may be involved in lipid vacuole formation. Myoepithelial cells surrounded alveoli. After carbamylcholine (CCh, 10–6, 10–5, and 10–3 M) stimulation, lipid materials within the membranous structures were frequently discharged by an exocytotic mechanism. Conspicuous deformation of glandular cells caused by vigorous contraction of myoepithelial cells was observed in isolated alveoli after 10–6M CCh stimulation, whereas the deformaties of glandular tissues perfused via vessels were small even after 10–3M CCh stimulation. Connective tissue between glandular alveoli inhibited unbridled myoepithelial-cell contraction. Fura-2/AM digital imaging analysis revealed that CCh stimulation caused an increase in Ca2+]c in isolated alveoli. The morphological reactions and changes in Ca2+]c were prevented by atropine. When extracellular calcium ions were absent, enhanced extrusion of lipid vacuoles, myoepithelial-cell contraction, and a rise in Ca2+]c after CCh stimulation were not observed. Nicotine and catecholamines had no effect on the secretion or on the dynamics of Ca2+]c. It can be concluded that acetylcholine elicits exocytosis in glandular cells and contraction of the myoepithelial cells of Harderian glands, accompanied by an increase in Ca2+]c. The dynamics of Ca2+]c of the gland alveoli are mostly dependent on extracellular Ca2+. |
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Keywords: | Harderian gland Ultrastructure Fura-2/AM digital imaging Calcium ion Carbamylcholine Myoepithelial cells Guinea pig |
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