Effect of cellular Ca2+ loading on alpha 1-agonist or protein kinase C activators-mediated stimulation of phosphorylase "a" in liver cells

Abstract

Long chain unsaturated fatty acids stimulate phosphorylase "a" activity in liver cells. Similar degree of activation was achieved by increasing cellular Ca2+ content or by treatment with agents other than oleate, like 1,2-diolein or phorbol esters, sharing in common their ability to activate protein kinase C. In Ca2+-loaded liver cells only phenylephrine was capable of inducing a further stimulation of phosphorylase "a" activity. It is concluded that: 1) The state of activation of protein kinase C may play a role in the hormonal control of liver glycogen metabolism; 2) alpha 1-agonist-mediated activation of phosphorylase "a" can occur by a mechanism which is not related to a Ca2+-dependent activation of protein kinase C.