Structural difference between luminal and lateral plasmalemma in pancreatic acinar cells.

Abstract

THE acinar cells of the pancreas, as well as other exocrine protein secreting cells, are highly polarised. Release of secretion products, which occurs by exocytosis (fusion of the secretory granule membrane with the plasmalemma (PM) followed by opening at the point of fusion1, is limited to the restricted portion of the cell surface facing the secretory lumen. It is still unclear whether this selective localisation of discharge depends on the specific properties of the luminal portion of the PM. Studies carried out in other cell systems have indeed revealed that regions of the PM where specialised functions are located can exhibit distinct characteristics2–5. But in the pancreas a comparative analysis of the secretory portion of the PM relative to the non-secretory portion has never been reported. By the use of freeze-fractture we have now observed that the luminal PM is different in structure from the remainder of the PM. Rather it is reminiscent of the membrane with which it is functionally associated, the membrane of the zymogen granule (ZG).