Hyposmolarity stimulates myeloperoxidase exocytosis from human polymorphonuclear leukocytes

Medium hyposmolarity induced in human polymorphonuclear leukocytes treated with cytochalasin B a rapid exocytosis of the lysosomal enzyme, myeloperoxidase (MPO), which was linearly proportional to the degree of hyposmolarity between a 5 and 30% decrease (r = 0.92, p less than 0.001). Cell viability was unaffected by the hyposmolarity. The kinetics of MPO exocytosis induced by opsonized zymosan (OZ) and hyposmolarity were indistinguishable; the combination of hyposmolarity and OZ was additive. Since hyposmolarity similarly stimulates a burst of hormone secretion by perifused adenohypophyseal and pancreatic islet cells, the authors suggest that hyposmolarity-induced exocytosis is a general cellular phenomenon.