Calmodulin dependency of calcitonin action on glucose-6-phosphatase and phosphorylase a activites in the liver of rats

Abstract

The calmodulin dependency of calcitonin (CT) action on glucose-6-phosphatase and phosphyorylase alpha activities in the liver of rats was investigated. A single sc administration of CT (synthetic [A1,7] eel CT; 80 MRC mU/100 g body weight) produced significant increases in calcium content and glucose-6-phosphatase activity in the hepatic microsomes of intact and thyroparathyroidectomized rats. These increases in enzyme activity were significantly inhibited by W-7 (100 microM), with a concentration which showed maximal effect. However, this inhibition was less than 50% of the enzyme activity increased by CT administration. Meanwhile, CT produced significant increases in calcium content and phosphorylase alpha activity in the hepatic glycogen particles from intact rats. However, this increase in enzyme activity was not influenced significantly by W-7 (100 microM), suggesting that the calcium ion may directly activate the enzyme. These results suggest that the increase in microsomal glucose-6-phosphatase activity of rat liver mediated by cellular calcium following CT administration may partly depend on calmodulin.