Differential effects of norepinephrine and phorbol ester on alpha-1 adrenergic receptor number and surface-accessibility in DDT1 MF-2 cells.
The short (5-60 min) and long (24 hrs) term effects of norepinephrine (10 uM) and the phorbol ester, 12-0-tetradecanoyl phorbol-13-acetate (10 nM), on total cellular and surface-accessible alpha-1 adrenergic receptor number were determined in DDT1 MF-2 smooth muscle cells. The density of alpha-1 adrenergic receptors was determined with [3H]-prazosin in a crude cellular homogenate (total cellular receptors) and in intact cells at 4 degrees C (surface-accessible receptors). Under basal conditions, all receptors were accessible to the cell surface at 4 degrees C. Short term norepinephrine exposure caused an approximately 40% decrease in surface-accessible binding without a change in total receptor number. Long term norepinephrine exposure caused a further decrease in surface-accessible binding, and an approximately 30% decrease in total receptor number. In contrast, phorbol ester had no effect on surface-accessible or total receptor number with either short or long term exposure. These data suggest that sequestration of cell surface alpha-1 adrenergic receptors is an early step in the process of agonist-mediated down-regulation. In DDT1 MF-2 cells, phorbol ester, alone, does not mimmick the effect of agonist on receptor sequestration or number.
Colucci
W S
WS
Department of Medicine, Brigham & Women's Hospital, Boston, MA 02115.
Akers
M
M
Wise
G M
GM
D002460:Cell Line; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D011224:Prazosin / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D011942:Receptors, Adrenergic, alpha; D013755:Tetradecanoylphorbol Acetate; D009638:Norepinephrine; D011224:Prazosin