Inhibition of hormone-stimulated ornithine decarboxylase activity by lithium chloride.
Effects of Li+ on hormone-stimulated ornithine decarboxylase (ODC) activity were determined in kidney and liver of rats treated with dexamethasone or prolactin (PRL) and also in cultured, PRL-stimulated Nb2 lymphoma cells. In both systems, LiCl led to rapid and marked decreases in ODC activity. The inhibitory effect of Li+ in exponentially growing Nb2 lymphoma cell cultures, measured at 45 min, was dose-dependent, ranging from 10% at 0.1 mM LiCl to 95% at 10 mM LiCl. Surprisingly, on continued incubation with 10 mM LiCl, the lymphoma cells partially overcame the inhibition, showing ODC activities which reached a maximal value of ca 50% of the control at 4.5 h. The inhibition by Li+ could not be reduced by adding myo-inositol to the culture medium. LiCl did not inhibit ODC activity when added to cell-free extracts of rat tissues and Nb2 lymphoma cells indicating it did not act directly on the enzyme; however, there is evidence that, in intact cells, Li+ enhances the rate of inactivation of the enzyme.
Richards
J F
JF
Department of Biochemistry, University of British Columbia, Vancouver, Canada.
Fox
K
K
Peng
T
T
Hsiao
J
J
Gout
P W
PW
D000818:Animals; D002712:Chlorides / Q000008:administration & dosage / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D007668:Kidney / Q000187:drug effects / Q000201:enzymology; D008094:Lithium / Q000008:administration & dosage / Q000494:pharmacology*; D018021:Lithium Chloride; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008223:Lymphoma / Q000188:drug therapy / Q000201:enzymology*; D009955:Ornithine Decarboxylase / Q000378:metabolism*; D011388:Prolactin / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013950:Thymus Gland / Q000187:drug effects / Q000201:enzymology; D014407:Tumor Cells, Cultured
D002712:Chlorides; D003907:Dexamethasone; D011388:Prolactin; D008094:Lithium; D009955:Ornithine Decarboxylase; D018021:Lithium Chloride