Phospholipid metabolism and intracellular Ca2+ homeostasis in cultured rat hepatocytes intoxicated with cyanide

The killing of cultured hepatocytes by 1 mM sodium cyanide was reduced by 100 microM chlorpromazine or cytochalasin B (25 micrograms/ml) or by lowering the pH of the culture medium to 6.0. In each case, ATP was depleted despite the decreased number of dead cells. The cell killing by cyanide was accompanied by an accelerated release of 3H-labeled arachidonate from phospholipids. Depletion of ATP by oligomycin did not accelerate phospholipid degradation or kill the hepatocytes. Chlorpromazine, cytochalasin B, and extracellular acidosis reduced the rate of phospholipid degradation in control cells as well as the increase that occurred with cyanide. The calcium ionophore A23187 increased phospholipid degradation and killed the hepatocytes. Chlorpromazine and extracellular acidosis, but not cytochalasin B, protected the cells and prevented the increased lipid degradation in response to A23187. After addition of cyanide, cytosolic free calcium ([Ca2+]i) did not change for 71 +/- 8 min, at which time it rose to a plateau of 683 +/- 210 nM within 10 min. A second and larger rise occurred after 84 +/- 8 min and before the death of the cells at 89 +/- 8 min. Treatment with 3.5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, as well as removal of extracellular calcium, prevented these late increases in [Ca2+]i without affecting the loss of viability. It is concluded that cyanide kills cultured hepatocytes by a mechanisms that is likely related to an accelerated degradation of phospholipids. This change in lipid metabolism is not mediated by a rise in [Ca2+]i but rather may relate to an alteration in the interaction between the cytoskeleton and the plasma membrane.