Altered binding properties of β-adrenergic receptors and lack of coupling to adenylate cyclase in P815 mastocytoma cells

Abstract

P185, a murine mastocytoma cell line, possesses β-adrenergic binding sites as assessed by using [ 3H]dihydroalprenolol (antagonist) and [ 3H]hydroxybenzylisoproterenol (agonist). The number of binding sites per cell was 29 000 for the agonist and 75 000 for the antagonist, as determined by direct binding assays and inhibition experiments on intact cells. On membrane preparations from the same cells, binding of alprenolol was only displaceable by antagonists, while stereospecific binding of hydroxybenzylisoproterenol was only displaceable by agonists. The P815 membranes also possessed an adenylate cyclase stimulated by Gpp(NH)p and NaF but not by l-isoproterenol. The intracellular cAMP level of intact cells was not modulated by l-isoproterenol or by l-epinephrine, but was increased by forskolin. These results suggest that the β-adrenergic receptor of P815 mastocytoma cells is non-functional. This may explain the failure of agonists to stimulate adenylate cyclase activity in these cells.