Effect of propranolol and related drugs on transmembraneous pH differences in liposomes

Propranolol (1-isopropylamino-3-(1-naphtoloxy)-propan-2-ol) a beta-adrenergic receptor blocking agent was found to cause changes of transmembraneous pH in liposomes prepared from Soy-lecithin and cardiolipin. When the external pH was neutral and the internum of the liposomes acidic, the drug decreased the pH gradient. When the externum was acidic and the internum neutral, the gradient was increased by the drug. The effect of butacaine was similar to that of propranolol, while procaine, timolol and practolol were ineffective. It is suggested that the charged form of propranolol is bound to the membrane and dislocates protons from binding sites in the membrane and that the uncharged form of propranolol penetrates the membrane. After penetration it could associate with protons in the intraliposomal compartment and hence increase the pH of the interior. Depending on the direction of the pre-existing proton gradient propranolol would thus be able to increase or decrease the pH difference across the liposomal membrane.