title: Acute effect of ethanol on hepatic reticular G6Pase and Ca2+ pool.
abstract: BACKGROUND
  Hydrolysis of glucose 6-phosphate (G6P) via glucose 6-phosphatase (G6Pase) enlarges the reticular Ca(2+) pool of the hepatocyte. Exposure of liver cells to ethanol (EtOH) impairs reticular Ca(2+) homeostasis. The present study investigated the effect of acute EtOH administration on G6P-supported Ca(2+) accumulation in liver cells.
  
  
  METHODS
  Total microsomes were isolated from rat livers acutely perfused with varying doses of EtOH (0.01, 0.1, or 1% v/v) for 8 minutes. Calcium uptake was assessed by (45) Ca redistribution. Inorganic phosphate (Pi) formation was measured as an indicator of G6Pase hydrolytic activity.
  
  
  RESULTS
  G6P-supported Ca(2+) uptake decreased in a manner directly proportional to the dose of EtOH infused in the liver, whereas Ca(2+) uptake via SERCA pumps was decreased by ~25% only at the highest dose of alcohol administered. The reduced accumulation of Ca(2+) within the microsomes resulted in a smaller inositol 1,4,5-trisphosphate (IP(3))-induced Ca(2+) release. Kinetic assessment of IP(3) and passive Ca(2+) release indicated a faster mobilization in microsomes from EtOH-treated livers, suggesting alcohol-induced alteration of Ca(2+) releasing mechanisms. Pretreatment of livers with chloromethiazole (CMZ) or dithiothreitol (DTT), but not 4-methyl-pyrazole prevented the inhibitory effect of EtOH on G6Pase activity and Ca(2+) homeostasis.
  
  
  CONCLUSIONS
  Liver G6Pase activity and IP(3) -mediated Ca(2+) release are rapidly inhibited following acute (8 minutes) exposure to EtOH, thus compromising the ability of the endoplasmic reticulum to dynamically modulate Ca(2+) homeostasis in the hepatocyte. The protective effect of CMZ and DTT suggests that the inhibitory effect of EtOH is mediated through its metabolism via reticular cyP4502E1 and consequent free radicals formation.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Jacobs-Harper
authors.forename: Ashlee
authors.initials: A
authors.lastname: Crumbly
authors.forename: Andrea
authors.initials: A
authors.lastname: Romani
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000431:Ethanol / Q000008:administration & dosage*; D005952:Glucose-6-Phosphatase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012156:Reticulocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*
chemical_list: D000431:Ethanol; D005952:Glucose-6-Phosphatase; D002118:Calcium