Internalization of atrial natriuretic factor by AtT-20 corticotropin-secreting cells.
Because extended exposure of AtT-20 corticotropin-secreting cells to atrial natriuretic factor (ANF) results in a desensitization of ANF-induced cGMP synthesis, we sought to establish whether pretreatment of AtT-20 cells with the atrial peptide also led to an internalization process. In fact, by coupling an ultrastructural approach to cryoultramicrotomy, ANF-immunoreactivity was detected at both the plasma membrane level and at intracellular sites in AtT-20 cells. Internalization was observed within 5 min at which time labelling was observed in the plasma membrane level, in vacuole-like structures in close proximity to the plasma membrane, in cytoplasmic matrix and sometimes in mitochondria. After 30 min exposure Golgi apparatus, mitochondria and nuclear euchromatin were also labelled. Following 1-4 hr, labelling in other cell compartments, e.g. lysosomal, was increased, while it was reduced in plasma membranes and vacuole-like structures. Secretory granules and endoplasmic reticulum were not labelled throughout the time course. Extraction of a intracellular [125I] ANF from AtT-20 cells following 4 hr incubation suggested that about 90% of the peptide was intact. The data suggest that internalization of ANF may serve to terminate the biological response associated with ANF receptor activation; subcellular distribution of internalized, intact ANF suggests that the peptide may have other, as yet unidentified, intracellular actions.
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D001692:Biological Transport; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D006651:Histocytochemistry; D007118:Immunoassay; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure
D009320:Atrial Natriuretic Factor; D000324:Adrenocorticotropic Hormone