Ultrastructural analysis of VIP internalization in rat beta- and acinar cells in situ.
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.
Anteunis
A
A
Unité Recherches sur les Peptides Neurodigestifs et le Diabéte, Institut National de la Santé et de la Recherche Médicale U.55, Paris, France.
Astesano
A
A
Portha
B
B
Hejblum
G
G
Rosselin
G
G
D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004705:Endocytosis; D006056:Golgi Apparatus / Q000378:metabolism; D007700:Kinetics; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D008854:Microscopy, Electron; D015388:Organelles / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D011919:Rats, Inbred Strains; D014617:Vacuoles / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
D014660:Vasoactive Intestinal Peptide