Three‐dimensional reconstruction of a small‐granule paracrine cell cluster in an adult hamster bronchus

Abstract

Amine precursor uptake and decarboxylation (APUD) small-granule cells were stained by periodic acid-Schiff (PAS)-lead hematoxylin in 0.5-micron etched Epon sections of adult hamster lung fixed for transmission electron microscopy. The leading edge of a small-granule cell cluster was identified in a segmental bronchus as a single PAS-positive cell. From 256 serial thin sections through its entirety, a three-dimensional wooden reconstruction of the cluster and morphometric estimates of the apical and basal surfaces, cell volume, and intracytoplasmic distribution of mitochondria and small granules was made. Of moderate size, the body consisted of 16 small-granule cells, 11 forming its ovoid core with five outlying cells diverging at the margin; these were pyramidal, possessing wide bases and thin apical processes. At the bronchial surface, processes from the 11-cell core emerged together, whereas the divergent cells emerged in groups of two and three. Ten Clara-like cells and one ciliated cell encircled the core. Altogether they formed a pseudostratified epithelium in contrast to the surrounding simple columnar epithelium. Deeper in the cluster, numerous cytoplasmic extensions interdigitated with those from adjacent cells, and toward the base the Clara-like and APUD cells were increasingly interposed. In marked contrast to the apical cytoplasm, the infranuclear cytoplasm of the latter was densely packed with ca. 1,000 A electron-dense granules; and the basal, presumptively secretory face of each cell was five to six times greater than the area exposed to the bronchial lumen. Judged by granule size and ultrastructure, only one APUD cell type was recognized in the reconstructed cluster. Beneath it many fibrocytic processes were separated from the APUD cells by only the thickness of the basal lamina. Two fascicles of smooth muscle approached the cluster within 0.4-0.8 micron. Unmyelinated nerve fibers came as close but contacted only the muscle. Capillaries, in contrast, came no closer than 15 micron from the base of the body. Evidently, 1) fibrocytes and smooth muscle are more likely targets for secretions from such a paracrine body than cells reached through the blood-stream, and 2) not all small-granule cell clusters are innervated.

Ontogeny of small‐granule APUD cells in hamster lung: A morphological study

“…that not all such bodies are innervated in adult lungs (Pearsall et al, 1985). Therefore, for the present the question of innervation in this species and the justification for using the term neuroepithelial bodies remain open.…”

Functional Live Cell Imaging of the Pulmonary Neuroepithelial Body Microenvironment

“…Application of high [K 1 ] o typically also evoked a Ca 21 response in the rounded 4-Di-2-ASP-negative cells that encircle NEBs, but not in other epithelial cells. Although a selective marker for Clara-like cells is currently not available, we were able to identify these cells as Clara-like cells based on their ex vivo staining characteristics, morphology, and typical location, selectively covering the lateral and apical surfaces of NEBs (8)(9)(10). Moreover, the [Ca 21 ] i rise provides a useful additional feature to discriminate Clara-like cells from the abundant Clara cells.…”

“…The neuroendocrine cells of NEBs are located between a variety of other epithelial cells such as Clara cells, ciliated cells, and small polyhedric basal cells. Electron microscopic studies have revealed that a specific type of nonciliated epithelial cells, the so-called Clara-like cells (8), is closely associated with NEBs (9,10). Although there may be species-and age-dependent differences in their appearance, electron microscopy revealed that Clara-like cells cover at least large parts of the apical and lateral surfaces of NEBs, with apical process of NEB cells reaching the airway lumen (8).…”

Phylogenetic aspects of the neuroepithelial bodies.

“…NEBs in eutherian mammals have been shown to occur on small mounds, in the hollow of pits and as part of the epithelium exhibiting no particular specialization (LAUWERYNS and PEUSKENS, 1972;CUTZ et al, 1978;PEARSALL et al, 1985). Similar arrangements have been observed in metatherian mammals (HALLER, pers.…”