Altered membrane fluidity in rat hepatocytes during endotoxic shock.

Steady-state fluorescence anisotropy measurements of the fluorescent hydrocarbon probe 1,6-diphenyl-1,3,4-hexatriene (DPH) were carried out in isolated hepatocytes of saline control and Salmonella enteritidis endotoxin (20 mg/kg) injected rats. Statistically significant differences were observed in the fluorescent anisotropy (rs) and membrane microviscosity (eta) values of control (rs = 0.107 +/- 0.004 (SEM), eta = 0.98 +/- 0.08, n +/- 6) versus endotoxin injected rat hepatocytes (rs = 0.134 +/- 0.005, eta = 1.43 +/- 0.08, n = 6, p < 0.001) at 37 degrees C. Fluidity was similarly lower in the isolated plasma membrane preparations from endotoxin-injected rat livers relative to control livers. When endotoxin-injected rats were treated with the calcium channel-blocker diltiazem, the anisotropy and microviscosity values were comparable to those obtained from control rats (rs = 0.152 +/- 0.003, eta = 1.00 +/- 0.003, n = 6). These measurements were made in animals five hours after endotoxin had been injected, and thus represent the in vivo effects of bacterial endotoxins. Temperature scan studies of DPH from 5-40 degrees C revealed that the membrane fluidity of endotoxin-injected rat hepatocytes was significantly lower than control hepatocytes at all temperatures investigated. The data suggest that endotoxin alters the membrane fluidity of hepatocytes, and that calcium-channel blockers can prevent the alteration. Our previous studies have shown that calcium channel blocker prevented endotoxin induced alterations in hepatic cellular regulation of Ca2+. Thus, cellular calcium homeostasis may be important in the maintenance of membrane fluidity and other membrane-associated transport functions.