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J. Cell Biol.,
Volume 141, Number 1, April 6, 1998 135-142
* Developmental Neurobiology Laboratory, RIKEN Brain Science Institute, Wako-City, Saitama 351, Japan; In polarized epithelial cells, agonists trigger
Ca2+ waves and oscillations. These patterns may be
caused by the compartmentalization of inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ pools into specific
regions. We have investigated the relationship between
the distribution of IP3 receptors (IP3Rs) and the spatiotemporal pattern of Ca2+ signaling in the duct cells
of the rat submandibular gland (SMG). Using immunofluorescence, although labeling was somewhat heterogeneous, the IP3Rs were colocalized to the apical pole
of the duct cells. Immunoelectron microscopy identified small apical vesicles bearing IP3R2 in some types of
duct cells. Real-time confocal imaging of intact ducts
demonstrated that, after carbachol stimulation, an initial Ca2+ spike occurred in the apical region. Subsequently, repetitive Ca2+ spikes spread from the apical
to the middle cytoplasm. These apical Ca2+ initiation
sites were found only in some "pioneer cells," rather than in all duct cells. We performed both Ca2+ imaging
and immunofluorescence on the same ducts and detected the strongest immunosignals of IP3R2 in the
Ca2+ initiation sites of the pioneer cells. The subcellular
localization and expression level of IP3Rs correlated
strongly with the spatiotemporal nature of the intracellular Ca2+ signal and distinct Ca2+ responses among the
rat SMG duct cells.
Department of
Molecular Neurobiology, The Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108, Japan; § Department
of Anatomy and Cell Biology, Faculty of Medicine, Kitasato University, Sagamihara-shi, Kanagawa 228, Japan; Department of
Anatomy, School of Medicine, Gunma University, Maebashi-shi, Gunma 371, Japan; and ¶ Tokyo Research Laboratories, Kyowa
Hakko Kogyo Co., Ltd., Machida-shi, Tokyo 194, Japan
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