Fine structure of the venom gland epithelium of the South American rattlesnake and radioautographic studies of protein formation by the secretory cells.

The South American rattlesnake venom gland is made up of secretory tubules lined by a simple columnar epithelium containing horizontal cells, mitochondria-rich cells, and the principal cell type, the columnar secretory cells. This cell has a round basal nucleus and abundant rough endoplasmic reticulum, the cisternae of which are variably distended with flocculent material containing many dense intracisternal granules. The supranuclear Golgi apparatus is spherical, with stacks of flattened saccules at the periphery and large vacuoles containing masses of dense material, and other dense granules in the center. Similar but smaller granules are present at the apex where they fuse with the microvillus-covered apical membrane and release their content into the lumen. Protein synthesis was studied in snakes injected with 3H-tyrosine and sacrificed at several times after injection. Radioautographs showed reactions at one half and one hour over the ribosomes and membranes of the rough endoplasmic reticulum. At two hours the immature face of the Golgi apparatus was labeled. At four hours Golgi saccules and vacuoles with dense masses (secretory granules) were labeled, and at eight hours the dense masses within the secretory granules were heavily labeled both in the Golgi region and in the apex near the lumen. Labeled material was found in the lumen at two days. Intracisternal granules were first labeled at eight hours, and by two days reactions remained only over the flocculent content and intracisternal granules of the rough endoplasmic reticulum. Thus, venom protein was synthesized on the rough endoplasmic reticulum, migrated through the Golgi apparatus and accumulated in the dense masses of the secretory granules, which moved to the apex and were extruded. The labeling of intracisternal granules at eight hours and two days after injection indicated a storage nature for these granules.