Ductal Epithelium of Submandibular Gland

In polarized epithelial cells, agonists trigger Ca 2 1 waves and oscillations. These patterns may be caused by the compartmentalization of inositol 1,4,5trisphosphate (IP 3 )-sensitive Ca 2 1 pools into specific regions. We have investigated the relationship between the distribution of IP 3 receptors (IP 3 Rs) and the spatiotemporal pattern of Ca 2 1 signaling in the duct cells of the rat submandibular gland (SMG). Using immunofluorescence, although labeling was somewhat heterogeneous, the IP 3 Rs were colocalized to the apical pole of the duct cells. Immunoelectron microscopy identified small apical vesicles bearing IP 3 R2 in some types of duct cells. Real-time confocal imaging of intact ducts demonstrated that, after carbachol stimulation, an initial Ca 2 1 spike occurred in the apical region. Subsequently, repetitive Ca 2 1 spikes spread from the apical to the middle cytoplasm. These apical Ca 2 1 initiation sites were found only in some “pioneer cells,” rather than in all duct cells. We performed both Ca 2 1 imaging and immunofluorescence on the same ducts and detected the strongest immunosignals of IP 3 R2 in the Ca 2 1 initiation sites of the pioneer cells. The subcellular localization and expression level of IP 3 Rs correlated strongly with the spatiotemporal nature of the intracellular Ca 2 1 signal and distinct Ca 2 1 responses among the