Localization and binding of reserpine in the membrane of adrenomedullary amine storage granules

Summary

The subcellular localization of ³H-reserpine persisting in the adrenal gland of the rat 18–60 h after parenteral administration was studied by differential and sucrose gradient centrifugation techniques.

This persistent reserpine is associated with the catecholamine storage granule. More specifically, the drug is exclusively localized in the vesicular membrane where it is attached by a firm bond which is not reversed by prolonged dialysis or by incubation with adrenomedullary granules from non-reserpinized rats.

Binding experiments conducted in vitro indicate that membranes isolated from bovine adrenomedullary granules or mitochondria bind reserpine at a single binding site with a molarity in these preparations of 9.4×10⁻⁹M/mg of protein with a binding constant of 4.7×10⁻⁷M. The in vitro binding of ³H-reserpine is reversible upon dialysis and has a low specificity since unlike the binding in vivo, it is not affected by preincubation of membranes with high concentrations of unlabeled reserpine. There was a very low affinity of reserpine for the intragranular constituents of adrenomedullary granules.

It is concluded that a rapid specific and irreversible binding of reserpine occurs in vivo in the membranes of amine storage granules which cannot be realized by bovine adrenomedullary granule membranes in vitro.