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

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Abstract
The calmodulin dependency of calcitonin (CT) action on glucose-6-phosphatase and phosphorylase .alpha. activities in the liver of rats was investigated. A single s.c. administration of CT (synthetic [A1,7] eel CT; 80 MRC [mouse radius calcifying] mU/100 g body wt) produced significant increases in Ca content and glucose-6-phosphatase activity in the hepatic microsomes of intact thyroparathyroidectomized rats. These increases in enzyme activity were significantly inhibited by W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide] (100 .mu.M), 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 Ca 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 .mu.M), suggesting that the Ca ion may directly activate the enzyme. Apparently the increase in microsomal glucose-6-phosphatase activity of rat liver mediated by cellular Ca following CT administration may partly depend on calmodulin.