IN VITRO INCORPORATION OF [3H]THREONINE AND [SH]GLUCOSE BY THE MUCOUS AND SEROUS CELLS OF THE HUMAN BRONCHIAL SUBMUCOSAL GLAND A Quantitative Electron Microscope Study

Incorporation of [nH]threonine and [3H]glucose by the mucous and serous cells of the human bronchial submucosal gland has been studied over 8 h using, for the first time, in vitro pulse labeling and electron microscope autoradiography. In assessing the autoradiographs, two methods were compared, the circle analysis and the recently described hypothetical grain analysis. Preliminary studies showed formaldehyde to be the most suitable fixative. Chemical analysis of tissue revealed that [3H]threonine was incorporated into the polypeptide moiety of the bronchial gland product and that metabolites of [SH]glucose were incorporated into the carbohydrate. Tritiated threonine was first localized in the endoplasmic reticulum of both mucous and serous cells and later migrated to the Golgi apparatus, while metabolites of [3H]glucose localized first mainly in the Golgi apparatus. From here, both radioactive precursors were next identified in vacuoles and, finally, in secretory granules. The mucous cell incorporated strikingly more of both radioactive precursors than the serous cell. Thus, it seems that oligosaccharides of mucous and serous cell glycoproteins are synthesized mainly in the Golgi apparatus and added there to the polypeptide core which is synthesized in the endoplasmic reticulum. The relationship of the mucous cell to the serous cell is discussed. It seems that under "normal" conditions each cell represents a different line but that injury may transform a serous cell into a mucous cell. The human bronchial submucosal gland includes two important types of secretory cell, the mucous and serous. These cells have different ultrastructural features (33) and have been shown by serial reconstruction to comprise their own individual and discrete regions of the gland (34). Histochemical studies have shown that the mucous cell contains four different types of acidic glycoprotein (25) that may occur either alone or in certain combinations but are not found together in a single cell. In the serous cell, however, both sialoand sulfomucin always occur together (26). In chronic bronchitis, the pattern of hypertrophy of mucous acini is rather different from that of serous acini 320 THE JOURNAL OF CELL BIOLOGY . VOLUME 67, 1975 , pages 320 344 on Jne 7, 2017 D ow nladed fom Published November 1, 1975