Role of calcium ions in rapid effects of L-thyroxine on phosphoinositide metabolism in rat liver cells.
The role of calcium ions in the L-thyroxine-induced initiation of hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) and also the course of releasing individual fractions of inositol phosphates and diacylglycerides (DAG) were studied in liver cells during early stages of the hormone effect. L-Thyroxine stimulated a rapid hydrolysis in hepatocytes of PtdInsP2 labeled with [14C]linoleic acid and [3H]inositol mediated by phosphoinositide-specific phospholipase C. This was associated with accumulation of [14C]DAG, total inositol phosphates, [3H]inositol 1,4,5-trisphosphate (Ins1,4,5P3) and [3H]inositol 1,4-bisphosphate (Ins1,4P2). Elimination of calcium ions from the incubation medium of hepatocytes did not abolish the effect of thyroxine on the accumulation of [14C]DAG and total [3H]inositol phosphates. Preincubation of liver cells with TMB-8 increased the stimulatory effect of L-thyroxine on the accumulation of [14C]DAG. During the incubation of hepatocytes in the presence of the hormone the content of 14C-labeled fatty acids did not change. The L-thyroxine-induced accumulation of [3H]Ins1,4,5P3 and [3H]Ins1,4P2 did not depend on the presence of calcium ions in the incubation medium of the cells.
Krasilnikova
O A
OA
Institute of Biology, Kharkov National University, Kharkov, 61077, Ukraine.
Kavok
N S
NS
Babenko
N A
NA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D004075:Diglycerides / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013974:Thyroxine / Q000494:pharmacology*; D014316:Tritium
D002250:Carbon Radioisotopes; D004075:Diglycerides; D010716:Phosphatidylinositols; D014316:Tritium; D013974:Thyroxine; D002118:Calcium