AJP - Gastrointestinal and Liver Physiology, Vol 264, Issue 2 187-G194, Copyright © 1993 by American Physiological Society
Pathway of insulin in pancreatic tissue on its release by the B-cell
M. Bendayan
Department of Anatomy, Universite de Montreal, Quebec, Canada.
Insulin was revealed in the extracellular space and blood capillaries of
the rat pancreas by applying protein A-gold immunocytochemistry. On the
discharge by the B-cell, insulin diffuses in the extracellular space and
interacts with the plasma membrane of all pancreatic cells. For the B-cell,
the interstitial microvillar plasma membrane domain was preferentially
labeled compared with the flat domain. In contrast, the digitations and
flat domains of the basal plasma membrane of the acinar cells were equally
labeled. In the endothelium, the labeling was superior in fenestrated areas
than in the high cytoplasmic ones, the fenestrae, the luminal and abluminal
plasma membranes being labeled. In the cytoplasmic areas the plasmalemmal
vesicles were significantly labeled; the intercellular junctions were not.
These results indicate that upon binding to the membrane, the transfer of
insulin across the capillaries occurs through both the fenestrations and
the vesicular system. The labeling of insulin in the subendothelial space
and blood capillaries decreased significantly from the insular to the
peri-insular and further to the teleinsular regions, demonstrating that
insulin levels, high in insular tissue, decrease very rapidly as insulin
circulates through and out of the pancreas. The pancreatic cells are thus
exposed to very high levels of insulin that vary according to the regions,
probably contributing to the topographical partition of the acinar
parenchyma into peri-insular and teleinsular tissues.
