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Acute Effect of Ethanol on Hepatic Reticular G 6 P ase and Ca 2+ Pool
Author(s) -
JacobsHarper Amy,
Crumbly Ashlee,
Romani Andrea
Publication year - 2013
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/j.1530-0277.2012.01933.x
Subject(s) - chemistry , microsome , homeostasis , hepatocyte , endoplasmic reticulum , calcium , ethanol , biochemistry , medicine , endocrinology , enzyme , in vitro , biology , organic chemistry
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 ( P i) 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 cy P 4502 E 1 and consequent free radicals formation.