Properties of rabbit pepsinogen granules.

Pepsinogen granules were isolated from the rabbit stomach using isoosmotic Percoll density gradients, low free calcium (10(-7) M), and conditions that minimize physical damage. These granules were enriched approximately eightfold with respect to pepsinogen and were free from contamination by mitochondria and endoplasmic reticulum. Electrophoretic examination shows pepsinogen to account for approximately 80% of the Coomassie Blue-stainable intragranular protein and the granule membrane to yield a simple spectrum of proteins similar to other granule systems. In addition to purity, the isolated granules displayed a high degree of osmotic stability at physiologic conditions of pH, temperature, and ionic strength. This stability suggests strict regulation of the granule electrolyte transport pathways, which are shown to include a Cl- conductance, Cl-/anion exchange, and a K+ conductance. These transport systems in the granule membrane are consistent with the promotion of primary fluid secretion. Furthermore, granule-mediated ion transport would allow the chief cell to couple fluid secretion directly to exocytotic pepsinogen secretion and flush the enzyme from the base of oxyntic glands.