Stimulation of CTP: phosphocholine cytidylyltransferase and phosphatidylcholine synthesis by calcium in rat hepatocytes.
The effects of Ca2+, ionophore A23187, and vasopressin on CTP:phosphocholine cytidylyltransferase were investigated. Cytidylyltransferase is present in the cytosol and in a membrane-bound form on the microsomes. Digitonin treatment caused release of the cytosolic form rapidly. Addition of 7 mM Ca2+ to hepatocyte medium resulted in a 3-fold decrease in cytidylyltransferase released by digitonin treatment (1.7 +/- 0.1 nmol/min per mg compared to 5.1 +/- 0.2 nmol/min per mg in the control). Verapamil, a calcium channel blocker, partially overcame this effect of Ca2+. Ionophore A23187 and vasopressin both mimicked the effect of Ca2+ and resulted in a decrease in cytidylyltransferase release (2.4 +/- 0.1 nmol/min per mg and 2.5 +/- 0.2 nmol/min per mg, respectively) compared to control (3.4 +/- 0.1 nmol/min per mg). In agreement with the digitonin experiments, incubation with 7 mM Ca2+ resulted in a decrease in cytidylyltransferase in the cytosol (from 4.0 to 1.2 mol/min per mg) and a corresponding increase in the microsomes (from 0.6 to 2.4 nmol/min per mg). Verapamil partially blocked this translocation caused by Ca2+. Ionophore A23187 and vasopressin also caused translocation of the cytidylyltransferase from the cytosol to the microsomes. The addition of Ca2+ also resulted in an increase in PC synthesis. With 7 mM Ca2+ in the medium, the label associated with PC increased to 3.8 +/- 0.1.10(6) dpm/dish from 2.7 +/- 0.1.10(6) dpm/dish after 10 min. PC degradation was also affected, since 7 mM Ca2+ in the medium resulted in an increase in LPC formation both in the cell and the medium. We conclude that high concentrations of calcium in the hepatocyte medium can cause a stimulation of CTP:phosphocholine cytidylyltransferase and PC synthesis in cultured hepatocytes.
Sanghera
J S
JS
Lipid and Lipoprotein Research Group, University of Alberta, Edmonton, Canada.
Vance
D E
DE
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D019916:Choline-Phosphate Cytidylyltransferase; D003600:Cytosol / Q000201:enzymology; D004072:Digitonin / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000096:biosynthesis* / Q000378:metabolism; D051381:Rats; D012995:Solubility; D014667:Vasopressins / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D010713:Phosphatidylcholines; D014667:Vasopressins; D000001:Calcimycin; D014700:Verapamil; D009713:Nucleotidyltransferases; D019916:Choline-Phosphate Cytidylyltransferase; D004072:Digitonin; D002118:Calcium