Altered hepatocellular Ca2+ regulation during hemorrhagic shock and resuscitation

The present study evaluated the effect of the benzothiazepine Ca2+ channel blocker diltiazem (DZ) on altered hepatocellular Ca2+ regulation and oxidant injury during hemorrhagic shock/resuscitation. In anesthetized, male Sprague-Dawley rats, hemorrhagic shock was induced by rapid blood withdrawal and maintaining the mean arterial blood pressure at 40 mm Hg over 60 minutes. Rats were then resuscitated with 60% of shed blood and threefold the shed blood volume of Ringer's lactate. At the end of ischemia, and 60 or 300 minutes after resuscitation, hepatocytes were isolated by liver collagenase perfusion. Hepatocellular Ca2+ exchange (Ca2+ex), rate of cellular Ca2+ influx (Ca2+in), and Ca2+ membrane flux (Ca2+flux) were determined using 45Ca incubation techniques. Hepatocyte oxidant injury was evaluated by fluorometrically measuring thiobarbituric acid reactive substances and oxidized/reduced glutathione. Both hemorrhage and hemorrhage/resuscitation increased hepatocellular Ca2+in, Ca2+ex, and Ca2+flux. In contrast to control and sham-operated rats, in vitro stimulation by the Ca2+ agonist epinephrine (100 nmol/L) of hepatocytes from either hemorrhaged or resuscitated rats did not further increase Ca2+in. Administration of DZ (.8 mg/kg) with resuscitation significantly decreased cellular Ca2+ex and Ca2+flux, but did not restore impaired epinephrine-induced Ca2+in. DZ prevented hepatocyte lipid peroxidation and glutathione oxidation. These findings suggest hepatocellular Ca2+ overload and impaired Ca2+ signaling during hemorrhage/resuscitation. Increased Ca2+ uptake could be because of a receptor-gated Ca2+ influx and/or oxygen-free radical induced membrane Ca2+ leaks.