Determination of mitochondrial calcium content in hepatocytes by a rapid cellular-fractionation technique. Alpha-adrenergic agonists do not mobilize mitochondrial Ca2+.
A rapid cellular fractionation technique [the preceding paper, Shears & Kirk (1984) Biochem. J., 219, 375-382] was employed to separate a mitochondria-rich fraction from hepatocytes within seconds. Mitochondrial Ca was estimated to be no more than 41% of total cell Ca. At least half of the mitochondrial Ca was present in an energy-dependent pool; 20% of total cell Ca was accessible to EGTA within 10s. The alpha-adrenergic agonist phenylephrine stimulated glycogen phosphorylase activity by 100% within 0.5 min and induced a loss of 20% of total cell Ca after 10 min from the EGTA-inaccessible pool. However, between 0.5 and 10 min after the addition of phenylephrine to hepatocytes there was no significant change in the Ca content of the mitochondria-rich fraction. Hepatocytes that were preloaded with Ca2+ during 90 min incubation at 0-4 degrees C expelled this cation during 20 min incubation at 37 degrees C. After this time, phenylephrine failed to alter the Ca content of a mitochondria-rich fraction. It is concluded that alpha-adrenergic agonists do not mobilize Ca2+ from hepatocyte mitochondria.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002458:Cell Fractionation / Q000379:methods*; D004533:Egtazic Acid / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D006005:Phosphorylases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D009840:Oligomycins; D010656:Phenylephrine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D004533:Egtazic Acid; D006005:Phosphorylases; D002118:Calcium