OBSERVATIONS ON THE LOCALIZATION OF LABELLED AMINO ACID IN MOUSE ADRENAL CHROMAFFIN CELLS AFTER THE INJECTION OF l-[4,5-3H]LEUCINE

Abstract

The intracellular localization of L-[4,5-3H] leucine in chromaffin cells has been observed using light and electron microscopic autoradiography and the association of the labelled amino acid with particular cell components confirmed by statistical analysis. By making observations at short intervals after a single intravenous pulse of [3H]leucine it has been possible to follow the movement of the isotope from the endoplasmic reticulum through the Golgi complex to the chromaffin granules. No evidence for movement of the label through the Golgi complex was observed in adjacent cortical cells. The time sequence of transport of the amino acid through the various cell organelles was very similar to that observed by previous workers in protein-secreting exocrine cells.

Physiological stimuli evoke two forms of endocytosis in bovine chromaffin cells

“…Another possibility is that both mechanisms retrieve the same membrane, but lead to different internal trafficking and recycling pathways. For example, it may be that the robust phase I endocytosis observed following single sAPs and at lower frequency stimulation results in a local recycling of membrane while the activity‐ and cyclosporin A‐sensitive phase II endocytosis leads to the slower endocytic recycling observed following heavier cell stimulation (Kobayashi et al 1978; Lingg et al 1983). Experiments combining measures of both surface and intracellular membrane trafficking will be required to test this possibility.…”

Multiple Forms of Endocytosis In Bovine Adrenal Chromaffin Cells

“…We argue that the slower one, termed compensatory endocytosis, exhibits properties that make it the most likely mechanism for membrane recycling during normal secretory activity. I n the neuroendocrine chromaffin cells of the adrenal medulla, exocytosis of catecholamines and peptides through the fusion of large dense core vesicles is followed by specific endocytosis of vesicle membrane components (Kobayashi et al, 1978;Benchimol and Cantin, 1982;Lingg et al , 1983;Phillips et al , 1983;Patzak and Winkler, 1986). The process by which exocytosis in neuroendocrine cells takes place and its kinetic description have received much attention and study in the past, but just recently has the process by which the secretory granule membrane components become recycled been kinetically described on the subsecond time scale (Neher and Zucker, 1993;Heinemann et al, 1994;Thomas et al , 1994;Artalejo et al, 1995;Burgoyne, 1995;Smith and Betz, 1996; for review see Henkel and Almers, 1996).…”