The Contrasting Role of Calcium Influx in Secretion Induced by Cell Swelling Can Differentiate Normal and Tumor-Derived Rat Pituitary Cells*

Abstract

We have evaluated whether cell swelling may be a generally useful technique to differentiate normal and neoplastic pituitary cells, making the comparison between normal lactotrophs and thyrotrophs and tumor-derived GH4C1 and MMQ cells. With 1.5 mM medium Ca2+, cell swelling induced by osmotically equivalent stimuli, 27% medium hyposmolarity or 80 mM isotonic urea, caused a prompt increase in both intracellular Ca2+ and hormone secretion by all cell types. Depletion of medium Ca2+ abolished the cell swelling-induced increase in intracellular Ca2+ in all cell types and hormone secretion in the tumor-derived cells. However, it enhanced hormone secretion in normal cells. The critical role of Ca2+ influx in osmotically induced secretion in neoplastic, but not normal, pituitary cells may reflect some fundamental alteration in the intracellular transduction system in tumor cells.