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 alpha-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 alpha-aminoisobutyric acid transport by epinephrine. In contrast, dihydroergotamine abolished and phentolamine diminished the induction of alpha-aminoisobutyric acid transport by epinephrine but did not decrease the stimulation of cAMP levels by epinephrine. Epinephrine dose response curves for cAMP and alpha-aminoisobutyric acid transport were similar. Once exposed to epinephrine, cells became refractory to further stimulation of cAMP levels by epinephrine.