Ultrastructural pathology of phalloidin-intoxicated hepatocytes in the presence and absence of extracellular calcium

The killing of cultured hepatocytes by phalloidin can be dissociated into two phases by manipulation of the Ca ²⁺ concentration of the medium. In the absence of extracellular Ca ²⁺, hepatocytes are injured but not killed by phalloidin. Addition of 1.8 mM Ca ²⁺ to the culture medium kills 60-70% of the cells by three hours. As an initial attempt to identify the mechanisms whereby Ca ²⁺ ions irreversibly injure phalloidin-damaged hepatocytes, the authors have examined the ultrastructural pathology of phalloidin-intoxicated liver cells in the presence or absence of extracellular Ca ²⁺. In the absence of extracellular Ca ²⁺ ions, the morphologic manifestations of phalloidin intoxication reflect entirely the interaction between phalloidin, microfilaments, and the plasma membrane. In the presence of Ca ²⁺ ions, three morphologic manifestations of the lethal effects of Ca ²⁺ are described: the swelling of mitochondria accompanied by the accumulation of dense, amorphous precipitates; a supercontracture of microfilaments, and a loss of volume control with intracellular edema and a change in cell shape. These alterations can be attributed to the known biologic actions of Ca ²⁺ ions on cellular structure and function. The present study allows, therefore, a preliminary identification of mechanisms by which extracellular Ca ²⁺ ions may mediate cell death in this as well as in other similar situations.