Regulation of hormone secretion by acute cell volume changes: Ca2+-independent hormone secretion

Exocytosis of intravesicular material should help a cell meet a relative ex tracellular hyposmotic challenge by expanding the plasmalemma through fusio n with vesicular membrane. Cell swelling evokes an immediate secretory burs t of hormones stored in secretory vesicles with dynamics indistinguishable from those induced by specific secretagogues. Hormone secretion induced by cell swelling is not associated with a rise in cAMP, IP3, or prostaglandins , and it is not depressed by inhibition of stretch mechanoreceptors or aqua porin channels. In contrast to most types of regulated secretion, that indu ced by cell swelling in normal cells does not require a rise in intracellul ar Ca2+ through opening L-type Ca2+ channels. However, such Ca2+ influx is essential for cell-swelling induced secretion in tumor-derived pituitary ce lls. Cell swelling induces universal secretion of exocytotic material. The response of cells specialized in osmoregulation is, however, different. Pos sible physiological significance: Consistent stimulation of secretion occur s with a 4% hyposmolar challenge. It is likely that fluctuations in osmotic pressure with resultant cell volume changes have a significant regulatory role in hormone secretion. Released hormones could also play an important r ole in the pathophysiology of ischemia. Exocytosis itself does not have an essential role in volume regulation. Copyright (C) 2000 S. Karger AG. Basel .