REGULATION OF GLYCOGEN-PHOSPHORYLASE ACTIVITY IN ISOLATED HUMAN HEPATOCYTES

Hepatocytes were isolated from human liver tissue by a two-step perfus ion technique. They were treated with vasopressin, angiotensin, ATP an d phenylephrine, which are known to be Ca2+-mediated glycogenolytic ag ents in rat liver tissue, and as a control, they were treated with the cyclic AMP-mediated hormones glucagon and isoproterenol. All agonists induce a time-dependent activation of glycogen phosphorylase. Glucago n and isoproterenol induce a somewhat higher degree of phosphorylase a ctivation compared with vasopressin, angiotensin, ATP and phenylephrin e, which all increase inositol tris-phosphate levels and have no effec t on the cyclic AMP levels. The total activity of glycogen phosphoryla se (a + b), amounting to 30 to 35 mU/mg protein, is found to be much l ower than that found in rat liver tissue. Because only minor differenc es could be found, we conclude that the regulation of glycogen phospho rylase in human liver tissue is basically the same as that found in ra t liver tissue.