Clara granules

Figure 10.1 Typical tracheo-bronchial and bronchiolar epithelia showing the major cell types. The tracheo-bronchial epithelium showing the pseudostratified nature of the columnar epithelium, principally composed of ciliated cells (C), interspersed with goblet cells (G), brush cells (Br), serous cells (S), Kulchitsky s cells (K) and basal cells (B). The bronchiolar epithelium showing the cuboidal nature of the epithelium, principally composed of ciliated cells (C), Clara cells (Cl) and infrequent basal cells. Muc = mucus Ci = cilia N = nucleus Sec = secretory granules.

In the sheep, Mariassy and Plopper (1983) observed 6 distinct, granule-containing secretory cells 4 mucous cell categories (M1-M4), serous cells, and nonciliated bronchiolar (Clara) cells. 

Fig. 65. Prominent endoplasmic reticulum and ovoid electron-dense secretory granules in the apical cap of a type 4 Clara cell from a bronchiole (block 465) of a male rat (No. 5/104 E) which inhaled 71.5 mg trimethylol melamine (Madurit) dust/1 for a total of 32 h 30 min on 4 consecutive days. Fixed under pentobarbital anaesthesia (30 mg/kg) by intratracheal instillation of 2.5 % glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.4) before opening the thorax. Postfixation with 1 % osmium tetroxide in sodium cacodylate buffer. Embedded in Epon 812 and sectioned at 50 nm. Lead citrate and uranyl acetate. Plate 4050...

From three-dimensional reconstruction of rat nonciliated bronchiolar (Clara) cells. Young et al. (1986) found a significant polarisation of the multivesicular bodies toward the Golgi. This is consistent with a metabolic or a precursor-product relationship between these structures and secretory granules as has been proposed for the type II pneumo-cytes (Chevalier and Collet 1972). 

Guanyhn, a peptide involved in the activation of gu-anylate cyclase C is exclusively confined to the Clara cells. In cattle, guinea pig and rat, Cetin et al. (1995) found guanylin immunoreactivity in a distinct population of secretory granules mostly loca-Used underneath the apical cell membrane. 

Streptozotocin (75 mg per kg body weight) markedly decreased the number of dense oval granules in the Clara cells of the rat (Plopper and Mori-SHiGE 1979). When present, they were usually smaller in size, but generally retained their electron density. The rode-shaped granules present in the apical portion of the Clara cell increased in number six or more were observed in 28 of the 57 cells examined. Therapy with insulin successfully reversed changes produced by streptozotocin-induced diabetes. 

Cobalt aerosols inhaled by rats at a concentration of 2.1210.55 mg/m for 5 h per day on 4 consecutive days induced Clara cell hypertrophy with abundant rough endoplasmic reticulum and electron lucent glycogen granules which were normally absent in adult rats (Kyono et al. 1992). At 8 days after exposure, the long strands of rough endoplasmic reticulum had disappeared. 

Ascorbic acid having the unique property of reducing an acidified solution of silver nitrate almost instantly (Gomori 1952, p.90), in the granule layer of the human cerebellum can only be detected in a few glial cells (Clara 1942, 1953). 

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