Radioautographic characterization of successive compartments along the rough endoplasmic reticulum-Golgi pathway of collagen precursors in foot pad fibroblasts of [3H]proline-injected rats.

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Abstract
Young rats given an i.v. injection of [3H]proline were killed at successive times from 4-80 min later. Fibroblasts from the front foot pad were radioautographed; Ag grains were counted over several of the organelles and the results were expressed as percent radiolabel/unit volume. These percentages reached a peak over rough endoplasmic reticulum cisternae at 4 min, intermediate vesicles and tubules at 10 min, spherical distensions of cis-side Golgi saccules at 20 min, cylindrical distensions of trans-side saccules betweeen 40 and 60 min, and secretory granules at 60 min. The succession of peaks apparently corresponds to the migration pathway of collagen precursor proteins within fibroblasts; i.e., the proteins synthesized in rough endoplasmic reticulum are delivered by intermediate vesicles and/or tubules to the spherical distensions of cis-side saccules, somehow pass from there to the cylindrical distensions of trans-side saccules and, finally, are carried by secretory granules to the extracellular space.