Effect of diltiazem on altered cellular calcium regulation during endotoxic shock

Cellular free and exchangeable Ca2+ were quantitated in livers of rats injected with saline (control), Salmonella enteritidis endotoxin (20 mg/kg), or diltiazem (0.8-1.2 mg/kg) plus the endotoxin (20 mg/kg). Injection of endotoxin alone resulted in signs of endotoxic shock in animals 5 h later. All rats were killed 5 h postinjection, and their livers were excised. Hepatocytes were prepared for the measurement of cytosolic [Ca2+] under basal and hormone-stimulated (1 and 10 microM epinephrine) conditions by means of quin 2 fluorescence technique. Liver slices were labeled with 45Ca, and the radioactivity was washed out to determine cellular exchangeable Ca2+. The apparent basal level of cytosolic Ca2+ in endotoxic rat hepatocytes [525 +/- 92 (SE) nM] was significantly (P less than 0.05) higher than in controls (146 +/- 23). A significant increase in the basal [Ca2+] occurred after stimulation with epinephrine in controls but not in endotoxic rat hepatocytes. In the endotoxic rats receiving diltiazem, basal [Ca2+] was significantly lower than in rats given endotoxin alone, and a significant elevation of cytosolic [Ca2+] with epinephrine also occurred. The cellular exchangeable Ca2+ in endotoxic rats (564 +/- 27 nmol/g) was significantly higher than in controls (427 +/- 23). Diltiazem treatment of endotoxic rats restored the exchangeable Ca2+ level to that found in controls. The endotoxic accumulation of cellular Ca2+ and its restoration toward control levels by diltiazem could be due to catecholamine-mediated Ca2+ influx and its blockade by diltiazem.