AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 4 689-G697, Copyright © 1989 by American Physiological Society

ARTICLES

Ultrastructural analysis of VIP internalization in rat beta- and acinar cells in situ

A. Anteunis, A. Astesano, B. Portha, G. Hejblum and G. Rosselin
Unite Recherches sur les Peptides Neurodigestifs et le Diabete, Institut National de la Sante et de la Recherche Medicale U.55, Paris, France.

We perfused the pancreas with 125I-labeled vasoactive intestinal peptide (VIP) to follow the concomitant distribution of radioactivity in beta- and acinar cells as a function of time. This distribution was quantitated by computer-assisted analysis of high-resolution video autoradiographs. Density labeling was expressed as normalized specific activity (disintegration density per volume density). Immediately after a 4-min perfusion of 125I-VIP, labeling in beta-cells was mainly concentrated on the cell surface and peripheral tubules and vesicles. After three 30-s pulses of 125I-VIP, separated by intervals of 3.5 min of buffer perfusion, lysosome-like structures were heavily labeled. When VIP internalization was prolonged, labeling was similar to that observed with the 4-min perfusion, indicating a high VIP disposal rate in the lysosome-like structures. In acinar cells, labeling persisted on the surface and the early vacuolar system. We conclude the following: 1) an active endocytotic system, linked to the transport and sorting of a neuromediator, is present in beta-cells; and 2) the differences between the distribution of labeling in acinar and beta-cells suggest that the regulation of VIP internalization is tissue specific.

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