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Epinephrine
Hepatocytes vs. Myocytes
By Elisabeth Harrell
5/24/2017
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• Epinephrine acts to increase the breakdown of glycogen in liver and muscle
tissues and its conversion to glucose
• In the liver, the glucose exported to blood circulation
• In muscles, the glucose enters glycolysis for conversion to energy
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Page 607
The glycogen targeting protein GM in a glycogen granule can be phosphorylated at two
different sites. When phosphorylated by the action of PKA resulting from the action of
epinephrine on a cell, glycogen phosphorylase is released from inhibition.
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Page 429 Action of epinephrine in hepatocytes
Page 604 Action of epinephrine in myocytes
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Footer Text
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Two pathways for epinephrine to activate Glucogen Phosphorylase in hepatocytes
The first uses adenylate cyclase  cAMP
 PKA phosphorylase kinase a
The second uses phospholipase C IP3 + DAG
 Ca2+  phosphorylase kinase b
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Epinephrine can have either a stimulatory
or inhibitory effect on muscle action
It has a stimulatory on
-adrenergic receptors
It has an inhibitory effect on
-adrenergic receptors
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