Physiological roles of the calcium wave for the regulation of fluid and electrolytes secretion in salivary cells

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1. Cell shrinkage and chloride secretion induced by calcium signal.(1) Calcium oscillation by the application of 0.1-0.25 uM carbachol was observed at the apical region of parotid cells. The calcium oscillation spreaded as a wave toward the basal area and induced a slow shrinkage.(2) 0.5 uM carbachol elicited a transient calcium wave and a rapid shrinkage after ~1 sec after reaching the calcium wave to the basal area.(3) 0.5 uM carbachol also elicited a rapid chloride secretion with a similar time course as the shrinkage.(4) lonomycin induced a large calcium response at the basal area and caused a slow shrinkage.These results suggest that the calcium response at the apical area is particularly important to induced fluid and electrolytes secretions.2. Examination of AQP subtype in rat parotid cells.Western blot confirmed the AQP-5 is expressed in the cell type.3.Calcium wave with incremental agonist stimulations.(1) We visualized the functional intracellular calcium stores with multi-photon laser microscopy. In addition, the photobleaching assay revealed that calcium stores at the apical and basal area are continuous.(2) Effects of submaximal concentrations of 1P3 on the calcium release and uptake indicate that the function of IP_3 receptors is suppressed by the decrease in calcium concentrations within the store.The present study clarified that calcium-regulating system in salivary cells act to maintain the spatiotemporal pattern of calcium response, and allowed to initiated it from the apical area. It is speculated that the optima I salivary secretion is induced with this patterned calcium signal.