Changes in Beta-Adrenoceptor Binding Properties and Receptor-Cyclase Coupling During in Vitro Maturation of Rat Reticulocytes

Abstract

The loss of β-adrenergic responsiveness during reticulocyte maturation was studied under tissue culture conditions in a defined cell population from rats. Initial β-receptor density and receptor-mediated cAMP formation in culture medium (RPMI 1640) exceeded the values obtained in isotonic KC1-buffer by 56 and 120 % respectively. During cell cultivation receptor density and hormonal responsiveness decreased rapidly by 40-50 % of their initial values within the first 20 h. In the following 3 days the rate of loss varied between 10 and 15 %/d. The same time course was observed for the maturation-dependent decrease in forskolin-stimulated cAMP formation. ATP depletion of cultivated cells caused a complete and irreversible loss of cAMP response within 90 min. Our results indicate that cell metabolism regulates the strength of the hormonal response. A defect in adenylate cyclase or in cyclase N-protein interaction seems to be rate-limiting for the functional inactivation of the β-adrenergic system during reticulocyte maturation.