Regulation of Clara cell 10 kD protein secretion by pilocarpine: quantitative comparison of nonciliated cells in rat bronchi and bronchioles based on laser scanning confocal microscopy.

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Standard immunohistochemical techniques and laser scanning confocal microscopy were used to assess changes in the abundance of Clara cell 10 kD protein (CC10) within granules and endoplasmic reticulum of rat nonciliated cells after the administration of the secretagogue pilocarpine. Intracellular pools of CC10 were compared over time with time-matched controls at two airway levels, proximal bronchi and terminal bronchioles. Three zones of reflectance intensity (high, medium, and low), corresponding to different densities of CC10 were used to quantify changes in CC10 levels. We observed a shift in the abundance of CC10 from endoplasmic reticulum to granules 30 min after injection of pilocarpine. In addition, the depletion of granule-based CC10 occurred earlier in bronchial cells (30 min) than in bronchiolar cells (60 min). We also noted that the density of CC10 within the two cellular compartments remained steady even though the levels of CC10 dropped due to degranulation. Following degranulation, CC10 levels returned to near-control levels. In the absence of pilocarpine, the percentage of cell volume occupied by the granule-based CC10 indicated that two varieties of nonciliated cells exist in bronchial airways. However, administration of pilocarpine abolishes this difference in CC10 abundance. Our results demonstrate that bronchial cells respond sooner to the secretagogue than do their bronchiolar counterparts and/or possess biosynthetic capabilities that are more easily overwhelmed than those of the terminal bronchiolar cells. These differences suggest that proximal nonciliated cells are distinct from distal nonciliated cells.

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