Characterization of the [3H]-desipramine binding site of the bovine adrenomedullary plasma membrane

The specific (i.e. nisoxetine-sensitive) binding of [3H]desipramine was studied in membranes prepared from bovine adrenal medullae. (1) [3H]desipramine bound reversibly and with high affinity (KD = 2.8 nmol/l) to a single class of non-interacting binding sites (Hill coefficient = 0.96); the maximal number of binding sites (Bmax) was 2.1 pmol/mg protein. (2) Binding of [3H]desipramine was dependent on [Na+] and [Cl-]. Increasing the concentrations of these ions increased binding. (3) Substrates and inhibitors of the neuronal noradrenaline transport system (uptake1) inhibited binding of [3H]desipramine with a rank order of potency typical for an interaction with the uptake1 carrier. The characteristics of [3H]desipramine binding remained essentially unchanged after solubilization of adrenomedullary membranes with the non-ionic detergent digitonin. The results indicate that the plasma membrane of bovine adreno-medullary cells is endowed with the neuronal uptake1 transporter.