The Development of Intracellular Membranes Concomitant with the Appearance of HCL Secretion in Oxyntic Cells of the Metamorphosing Bullfrog Tadpole

Abstract

Bullfrog tadpole stomachs of various metamorphic stages were examined to determine the fine-structural development of oxyntic cells and to correlate observed morphological development with the capacity to secrete HCl. It was found that in vitro tadpole stomachs can consistently be stimulated to secrete acid by stage XXIV of metamorphosis, when tail reabsorption is nearly complete. Concomitant with the appearance of HCl secretion, identifiable oxyntic cells were found in the gastric glands. Prior to stage XXIV (stages XXI and XXII) the majority of cells present in the developing gastric glands exhibit features of cytological organization characteristic of undifferentiated cells: large nuclei, relatively scantry cytoplasm, and numerous ribosomal particles within the cytoplasmic matrix. The newly differentiated oxyntic cells of stage XXIV tadpole stomachs are recognizable by the accumulation of tubular members of the smooth-surfaced endoplasmic reticulum in the apical portion of the cells. These membranous structures appear to be formed by the Golgi complex which is extremely elaborate at this stage of development. As the animals complete metamorphosis (stage XXV) further development of the oxyntic cells occurs, especially the elaboration of the tubular components of the smooth-surfaced endoplasmic reticulum. The abundance of these membranous tubules within the apical cell regions and the pattern of their packing is similar to that observed in oxyntic cells of adult frogs. Also consistent with studies on adult frogs, structural alterations associated with HCl secretion were seen in the later stages of metamorphosis. In stages XXIV and XXV tadpole stomachs, which had been stimulated to secrete acid by addition of histamine, the apical surfaces of oxyntic cells were invested with long filamentous microvilli which projected into the glandular lumen. These observations support the hypothesis that membrane transformations play an integral role in the mechanism of HCl secretion and they implicate the morphogenesis of the smooth-surfaced endoplasmic reticulum as a basic prerequisite in the development of gastric secretory function.