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.