Calcitonin Action on ATP Citrate Lyase Activity in the Hepatic Cytosol of Fed Rats and Its Calcium-Calmodulin Dependency

Summary

The effect of calcitonin (CT) on ATP citrate lyase activity in the hepatic cytosol was investigated after a single subcutaneous administration of the hormone to fed rats. Administration of CT (synthetic [Asu^1′7] eel CT; 80 MRC mU/100 g body weight) produced significant increases in ATP citrate lyase activity and calcium content in the hepatic cytosol of intact and thyroparathyroidectomized rats. Those alterations were also observed with the dose of CT at physiological level. The increased cytosolic ATP citrate lyase activity resulting from CT administration was prevented by treatment with 10 μM EGTA. This enzyme activity was restored by addition of calcium ion (2.5-10 μM). The rise in enzyme activity of CT-treated rats was markedly reduced by the presence of W-7 (10 and 100 μM), a calmodulin inhibitor, in the enzyme assay system, while that of control rats was not significantly altered by the drug. These results suggest that CT increases ATP citrate lyase activity in the hepatic cytosol of fed rats, and that this hormonal regulation may depend on calmodulin, and be mediated through raised calcium in the cytosol.

Key-Words

Calcitonin - ATP Citrate Lyase - Calcium - Calmodulin - Rat Hepatic Cytosol