AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 4 539-R546, Copyright © 1988 by American Physiological Society
Characterization of glucagon and catecholamine effects on isolated sheep hepatocytes
C. Morand, C. Yacoub, C. Remesy and C. Demigne
Laboratoire des Maladies Metaboliques, Institut National de la Recherche Agronomique, Theix, France.
The purpose of this study was to characterize the glycogenolytic response
to catecholamines and glucagon in isolated sheep hepatocytes. In this
species, epinephrine appeared to exert its action on hepatic glycogenolysis
by altering the cytosolic concentrations of both adenosine 3',5'-cyclic
monophosphate (cAMP) and Ca2+. In contrast to results obtained in rat
hepatocytes, glucagon failed to induce a rise in free cytosolic Ca2+ in
sheep liver. Experiments on isolated hepatocytes or on liver plasma
membranes showed that in sheep, glucagon was more efficient than
epinephrine in promoting the production of cAMP. In the presence of
glucagon or epinephrine, the activation of the glycogen phosphorylase a
always appeared greater in sheep than in rat liver cells, whereas the
variations in cellular cAMP were quite limited in sheep. The alpha 1- and
beta-agonists (phenylephrine and isoproterenol) were alone as efficient as
epinephrine in promoting phosphorylase a activation in sheep hepatocytes.
All these results indicate the existence in sheep liver of a glycogen
phosphorylase highly responsive to hormones.
