Redistribution of clathrin heavy and light chains in anoxic pancreatic acinar cells

In the present study, antibodies directed against clathrin light (33 kDa-36 kDa) and heavy (180 kDa) chains were used to confirm, by immunocytochemistry, that coated vesicles increase in number in the exocrine cells of pancreatic lobules incubated under anoxic (N2) conditions. The same antibodies were used to check whether or not the fibrillar aggregates, which appear under the same conditions on the cis side of the Golgi stacks of these cells, contain clathrins. By immunofluorescence, clathrin light chains were localized among zymogen granules and in small masses at the periphery of the Golgi complex in acinar cells incubated under N2. By electron microscopy, antibodies for light and heavy chains reacted with numerous coated vesicles located in clusters on the trans side of the Golgi stacks, scattered individually or in small clusters among zymogen granules throughout the apical region of the cell, and associated with both the apical and basolateral plasmalemma of the exocrine cells incubated under N2. The fibrillar aggregates cis to the Golgi complex stained less intensely and much less uniformly than the coats of the coated vesicle population. These findings suggest that the fibrillar aggregates which characteristically appear on the cis side of the Golgi stacks under anoxic conditions contain only small amounts of focally distributed clathrins. Their main components are probably other proteins whose relationship (if any) to clathrins and other clathrin cage constituents remains to be investigated. The findings also indicate that pancreatic acinar cells redistribute large amounts of clathrin, presumably from preexisting pools, when the transport of secretory and other proteins into the Golgi complex is inhibited. In control cells (incubated under O2-CO2), clathrin antigens had the same structural associations as in anoxic cells but the reactive sites were considerably less numerous and the reaction less intense.