The effects of the potato glycoalkaloids alpha-chaconine, alpha-solanine and tomatine on the intracellular free Ca2+ concentration were studied in undifferentiated mouse neuroblastoma x rat glioma hybrid NG 108-15 cells, mouse-skin fibroblastoma L-929 cells and mouse Balb/3T3 cells by using the Ca2+-sensitive fluorescent dye Fura-2. In all cultured cells treated with the alkaloids the intracellular Ca2+ concentrations were raised in a dose-dependent manner. The Ca2+ influx evoked by alpha-chaconine could not be prevented by metal ions or by inhibitors of Ca2+ transport across membranes such as voltage-operated channel antagonists, muscarinic and nicotinic antagonists, or Na+ and K+ channel blockers. The concentrations of alpha-chaconine, alpha-solanine and tomatine that gave half-maximal response (ED50) in NG 108-15 cells were 12.0, 72.0 and 1.8-mu-M, respectively. ED50 values in L-929 cells were 10.2-mu-M for alpha-chaconine and 65-mu-M for alpha-solanine and in Balb/3T3 cells the ED50 values were 9.5-mu-M for alpha-chaconine and 66-mu-M for alpha-solanine. These findings support the hypothesis that the alkaloid-evoked Ca2+ influx is caused by destabilization of the cell membrane and attribute a more important role to alpha-chaconine than alpha-solanine in potato poisoning. Fluorescence measurement of the free Ca2+ concentration in the cytoplasm therefore represents a useful tool for the evaluation of pharmacological properties of potato alkaloids in vitro.
