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Calcium signalling in tissue: diversity and domain-specific integration of individual cell response in salivary glands

¹ Department of Anatomy, School of Medicine, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan
² Department of Pharmacology, School of Medicine, Sapporo Medical University, South 1, West 17, Sappro 060-8556

^* Author for correspondence (e-mail: segawa{at}kitasato-u.ac.jp )

Organ function requires coordinated multicellular activities, which may require proper control of cell signalling dynamics at the supracellular level. By using high-speed confocal microscopy, we studied how calcium signalling is organised in the dissociated rat parotid gland. Salivary gland function is accomplished primarily by the compartmentalized epithelial domains, acini and ducts, the former involved in the production of primary saliva and the latter involved in its modification. Upon muscarinic stimulation with carbachol, both domains showed an increase in intracellular free calcium concentration ([Ca²⁺]i) with distinctive spatiotemporal kinetics, as indicated by the fluo-3 fluorescence. Acini responded initially, and the ducts followed with a time lag of more than 0.3 second. Cells comprising an acinus responded synchronously, whereas those in the ducts responded heterogeneously with respect to the latency period, magnitude of response and the requirement of extracellular calcium to raise [Ca²⁺]i. ATP also elicited a non-synchronous [Ca²⁺]i response in the duct domain, under a pattern different from that of carbachol. The synchronous oscillations seen in the acinar domain were made asynchronous by octanol, an agent known to inhibit gap-junction function. Accordingly, a gap junction component, connexin 32, was immunolocalised predominantly between the acinar cells. Moreover, expression of the type 2 inositol (1,4,5)-trisphosphate receptor [Ins(1,4,5)P₃R] was homogeneous in the acinar domain but heterogeneous in the duct domain. Together, these data suggest that the calcium signalling system in salivary glands is constructed specifically according to the tissue architecture.

Key words: Calcium signalling, Salivary gland, Gap junction, Ins(1,4,5)P₃ receptor, Epithelia

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