SPONTANEOUS CALCIUM OSCILLATIONS AND MECHANICALLY AND CHEMICALLY-INDUCED CALCIUM RESPONSES IN MAMMARY EPITHELIAL-CELLS

Changes of intracellular calcium activity (Cai(2+)) in mouse mammary epithelial cells in primary culture (normal) and in an established cell line (MMT060562, cancerous) were investigated by microfluorometry and image analysis of fura-2 fluorescence. In both types of cells, some populations exhibited occasional Cai(2+) oscillations with a period of 50 - 160 s. Slight mechanical stimulation of a cell with a fine glass pipette induced a Cai(2+) increase, which spread from the stimulated cell to the surrounding cells with a speed of 7-12 mum/s. ATP (> 1 mumol/1) and ADP. but not AMP induced a Cai(2+) increase in both cell types. Bradykinin was highly effective (> 10 nmol/l) only in the cancerous mammary epithelial cells. In Ca2+-free solution, all these Cai(2+) responses remained unchanged at the first application, and decreased abruptly at the second trial. La3+ (> 0.5 mmol/1) suppressed the response to ATP but not the response to bradykinin. Addition of extracellular Mn2+ rapidly quenched the fura-2 fluorescence in the cell even in a non-stimulated state. Influx of Mn2+ did not increase during Cai(2+) responses. These results indicate that the sources of Cai(2+) responses in mammary epithelial cells are intracellular stores, which exchange Ca2+ with the extracellular medium.