Evidence for the role of phosphorylase kinase, protein kinase C, and other Ca2+-sensitive protein kinases in the response of hepatocytes to angiotensin II and vasopressin.
Angiotensin II, catecholamines, and vasopressin can stimulate the phosphorylation of 10 hepatic cytosolic proteins via a Ca2+-linked, cyclic AMP-independent mechanism. To explore the role of known Ca2+-sensitive protein kinases in this response, [32P]PO4(3-)-labeled hepatocytes were stimulated with various agonists, the cytoplasmic proteins were separated on two-dimensional gels, and the resulting autoradiographs were computer analyzed. The role of phosphorylase kinase was examined using hepatocytes from gsd/gsd rats which are deficient in this enzyme. The phosphorylation state of phosphorylase was not increased by glucagon, angiotensin II, or vasopressin in hepatocytes from the gsd/gsd animals. The phosphorylation state of all other substrates was changed by glucagon or the Ca2+-linked hormones to the same extent in gsd/gsd hepatocytes as in normal Wistar controls, suggesting that phosphorylase kinase plays a restricted role in the hormone response. The role of the Ca2+- and phospholipid-sensitive protein kinase (protein kinase C) was examined by stimulating hepatocytes with phorbol esters which are thought to activate protein kinase C by substituting for diacylglycerol. Phorbol esters increased the phosphorylation state of 3 of the 10 substrates affected by angiotensin II or vasopressin, but did not stimulate Ca2+ fluxes in hepatocytes. Treatment of hepatocytes with the Ca2+ ionophore A23187 mimicked the effect of the Ca2+-linked hormones on the phosphorylation of the other 7 substrates. The results demonstrate that at least three Ca2+-sensitive protein kinases are involved in the response of hepatocytes to Ca2+-linked hormones. Since these kinases can be activated independently by phorbol esters or A23187, the results imply that hormones such as vasopressin generate two intracellular messengers, diacylglycerol and Ca2+ ion.
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D010764:Phosphorylase Kinase / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D014667:Vasopressins / Q000494:pharmacology*
D014667:Vasopressins; D000804:Angiotensin II; D011494:Protein Kinases; D010764:Phosphorylase Kinase; D011493:Protein Kinase C; D002118:Calcium