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

Abstract

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.

Ultrastructural simultaneous localization of vasoactive intestinal polypeptide immunoreactivity and the acetylcholine-like cation in rat endocrine pancreas.

“…VIP has also been shown to modulate the action of glucose on the release of insulin, glucagon and somatostatin (SCHEBALIN et al, 1977;SZECOWKA et al, 1980SZECOWKA et al, , 1983. In this case, VIP likely acts as a neuromediator binding to the specific receptors on endocrine cells (ANTEUNIS et al, 1986(ANTEUNIS et al, , 1989. Therefore, the present data suggest a neural control of hormonal secretion by ACh and VIP, which are released from nerve endings in contact with endocrine cells.…”

“…Vasoactive intestinal polypeptide (VIP), confirmed in nerve endings of the islets of Langerhans (LARSSoN, 1979), may be implicated in neuro-endocrine transmission, as suggested by the presence of VIP receptors on endocrine cells (ANTEUNIS et al, 1986(ANTEUNIS et al, , 1989. VIP might also be subjected to neurosecretion into the blood capillaries of the islets (FUJITA and KOBAYASHI, 1979).…”

Stimulatory Transducing Systems in Pancreatic Islet Cellsa

“…Previously, the presence of specific VIP binding sites and receptor‐mediated active endocytosis was demonstrated on islet pancreatic B cells by Anteunis and coworkers. 2 Using electron microscopic autoradiography after perfusion of the pancreas with 125 I‐labeled VIP, they found that the VIP‐induced insulin release 7 was promoted directly. 2 Using the same approach, the presence of VIP receptors (VIP R) on glucagon cells was observed, (Fig.…”

“…2 Using electron microscopic autoradiography after perfusion of the pancreas with 125 I‐labeled VIP, they found that the VIP‐induced insulin release 7 was promoted directly. 2 Using the same approach, the presence of VIP receptors (VIP R) on glucagon cells was observed, (Fig. 1), indicating that the effect of VIP in stimulating the glucagon release 7 is direct.…”

“… ( Top ) Autoradiography of pancreatic A cells after perfusion of the whole pancreas with 125 I‐labeled VIP and processing of islet sections (80 nm) for ultrastructural examination according to a previously described method. 2 Briefly, 4.5 nM 125 I‐labeled VIP, was injected for 3 min at 10°C to restrict endocytosis. The reaction was stopped by the fixation perfusion with 2.7% glutaraldehyde plus 0.8% formaldehyde in 80 mM sodium cacodylate buffer, and the islet cells stained for 3 min at 20°C with 0.12 mM dithizone.…”