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

Abstract

The loss of beta-adrenergic responsiveness during reticulocyte maturation was studied under tissue culture conditions in a defined cell population from rats. Initial beta-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 beta-adrenergic system during reticulocyte maturation.

Analysis by cell hybridization of mechanisms that regulate β‐Adrenergic responses in reticulocytes and in differentiating erythroid cells

“…We have shown earlier that a shift in the relative levels of G, and Gi membrane proteins, mediating stimulating or inhibitory hormone effects on adenylate cyclase, may determine catecholamine sensitivity in erythroid cells during terminal differentiation (Moudry and Porzig, 1990b). The decrease of P-receptor-coupled responses in rat reticulocytes follows a characteristic biphasic time course (Montandon and Porzig, 1984a). The mechanism responsible for the rapid initial phase of loss, with a reduction in cyclase activity by 50% within 10 h, is completely unknown.…”