ABSlRACl The pathway and kinetics of the secretory protein transport in rat lacrimal exorbital gland have been established by an in vitro time-course radioautographic study of pulse-labeled protein secretion.The colchicine-sensitive steps have been localized by using the drug at various times with respect to the pulse labeling of proteins. Colchicine (10/IM) does not block any step of the secretory protein transport, but when introduced before the pulse it decreases the transfer of labeled proteins from the rough endoplasmic reticulum to the Golgi area, suppressing their temporary accumulation in the Golgi area before any alteration of this organelle is detectable. Moreover, colchicine inhibits protein release only from the secretory granules formed in its presence because the peroxidase discharge is diminished I h after colchicine addition, and the secretion of newly synthesized proteins is strongly inhibited only when colchicine is introduced before secretory granule formation.Morphometric studies show that there is a great increase of secondary lysosomes, related to crinophagy, as early as 40-50 rain after colchicine is added. However, changes in lysosomal enzymatic activities remained biochemically undetectable.We conclude that: (a) the labile microtubular system does not seem indispensable for protein transport in the rough endoplasmic reticulum-Golgi area but may facilitate this step, perhaps by maintaining the spatial organization of this area; and (b) in the lacrimal gland, colchicine inhibits protein release not by acting on the steps of secretion following the secretory granule formation, but by acting chiefly on the steps preceding secretory granule formation, perhaps by making the secretory granules formed in its presence incapable of discharging their content.From data obtained with various secretory tissues, it appears that the microtubular system could be involved in the secretory process (62). We have previously shown in rat lacrimal #ands that colchicine inhibited the release of newly synthesized proreins by impairing their intraceUular transport (9), and simultaneously induced a disorganization of the labile microtubular system. This latter effect could result from the shift of the equilibrium between microtubules and tubulin and from the impediment of microtubule assembly due to the colchicinetubulin complex (10). The intraceUular transport alterations produced by colchicine have also been observed in other tissues that produce exportable proteins (liver: 17, 52-55; pancreas B-]FIE JOURNAL Of CELL BIOLOGY • VOtUME 95 OCTOBER 1982 105-117 @The Rockefeller University Press -0021-9525/82/10/0105/13 $1.00 cells: 36, 37; fibroblasts: 12, 14, 38; anterior pituitary: 1, 26, 48; mammary gland: 30, 41, 42; parotid gland: 46; exocrine pancreas: 61; parathyroid gland: 11, 29). Although there is no definite proof, the hypothesis that both events (i.e., inhibition of protein secretion and disruption of labile microtubules) might be related by a causal effect is favored.The aim of the present work is to lo...

The internalization of the yolk proteins has been investigated by electron microscopy and cytochemistry in the oocyte of the trout which stores up large quantities of yolk. The oocyte evolution has been followed for 18 months in a homogeneous group of animals. Anionic ferritin has been injected during vitellogenesis. The results indicate that as in other oocytes the yolk proteins are absorbed by coated vesicles during vitellogenesis. But unlike most other oocytes the yolk proteins are then transferred via typical endosomes to a conspicuous lysosomal compartment built up very early at the onset of the cytoplasmic differentiation of the oocyte e.i. 10 months earlier. During vitellogenesis yolk progressively accumulates in this lysosomal compartment. Injected anionic ferritin follows the same pathway of internalization. These findings indicate that in this oocyte, the whole yolk cycle presumably represents an adaptation of a general cellular activity, the receptor-mediated endocytosis, largely amplified, sequenced and spread over several months.

Biochemical studies have shown that low doses of Cytochalasin D (CD) inhibit protein discharge evoked by isoproterenol, a beta-adrenergic inducer, in isolated lobules of Rat parotid gland. Ultrastructural and radioautographic studies reported here indicate that, when lobules are treated by CD before isoproterenol stimulation, the connection of secretory granules with the acinar lumen is indeed prevented, but fusion of membrane granules evoked by isoproterenol still occurs. This fusion takes place with vacuoles induced by CD and possibly with other granules.