3′:5′-Cyclic AMP: Independent Induction of Amino Acid Transport by Epinephrine in Primary Cultures of Adult Rat Liver Cells

Liver cells were obtained from adult rats by a collagenase perfusion technique and cultured as monolayers in serum-free media. Epinephrine and isoproterenol both induced large increases in intracellular adenosine 3′:5′-monophosphate (cAMP) within 1-2 min whereas epinephrine (but not isoproterenol) induced 2- to 3-fold increases in the rate of α -aminoisobutyric acid transport within 2-4 hr after a 1 hr lag. Propranolol abolished the increase in cAMP elicited by epinephrine and isoproterenol, but did not block the induction of α -aminoisobutyric acid transport by epinephrine. In contrast, dihydroergotamine abolished and phentolamine diminished the induction of α -aminoisobutyric acid transport by epinephrine but did not decrease the stimulation of cAMP levels by epinephrine. Epinephrine dose response curves for cAMP and α -aminoisobutyric acid transport were similar. Once exposed to epinephrine, cells became refractory to further stimulation of cAMP levels by epinephrine.