Abstract
Rauscher murine erythroleukemia cells, grown continuously in vitro, undergo erythroid differentiation in response to the hormone erythropoietin. Therefore, they serve as an important model system with which to examine critical biochemical aspects of this developmental process. Intact, uninduced Rauscher cells possess a functional beta- adrenergic receptor-adenylate cyclase complex. The adrenergic agonists, isoproterenol, epinephrine, and norepinephrine, exhibited activation constants (Kact) of 0.1, 0.5, and 20 mumol/L, respectively. Thus, the beta-receptor-cyclase complex of Rauscher cells is apparently one of the most sensitive of all erythroid cells reported thus far. The epinephrine-stimulated cyclic adenosine monophosphate (cAMP) response was inhibited by propranolol, alprenolol, and hydroxybenzylpindolol, with inhibition constants (KI) of 3.8, 2.2, and 0.1 nmol/L, respectively. Using [125I]-iodohydroxybenzylpindolol as ligand, uninduced Rauscher cells were shown to possess 1,100 receptors/cell, with an equilibrium dissociation constant (KD) of 400 pmol/L. Erythropoietin, but not dimethylsulfoxide, induction caused a specific increase in receptor density to 3,300/cell on differentiating Rauscher cells. This is the first demonstration of membrane receptor regulation by erythropoietin that may be important in the complex interplay of hormonal effects during erythropoiesis.
