The effects of the potato glycoalkaloids α-chaconine, α-solanine and tomatine on the intracellular free Ca2+ concentration were studied in undifferentiated mouse neuroblastoma × 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 α-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 α-chaconine, α-solanine and tomatine that gave half-maximal response (ED50) in NG 108-15 cells were 12.0, 72.0 and 1.8 μm, respectively. ED50 values in L-929 cells were 10.2 μm for α-chaconine and 65 μm for α-solanine and in Balb/3T3 cells the ED50 values were 9.5 μm for α-chaconine and 66 μm for α-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 α-chaconine than α-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.
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