Effects of propranolol and a number of its analogues on sodium channels

To assess the relative contributions that the sodium channel blocking activity of propranolol may play in a variety of its therapeutic applications, its effects were examined in vitro with a sodium channel specific 22Na+ uptake system, using rat brain membranes. Propranolol inhibited 22Na+ uptake in the rat brain membrane preparation by acting as a competitive inhibitor of the binding of the sodium channel opening agent veratridine, with an IC50 for this action of 6.5 microM. This is approximately one order of magnitude higher in concentration than that necessary for expression of the beta-adrenergic antagonism of propranolol. The binding of propranolol and its action to block sodium channels were demonstrably different from those of the neurotoxins tetrodotoxin and saxitoxin. Propranolol had effects on sodium channels that are similar, although not identical to those of the local anesthetics procaine and lidocaine. The concentrations of propranolol and a number of its analogues which produced 50% inhibition of 22Na+ uptake (IC50 values ranging from 4 to greater than 100 microM) were similar to the concentrations of these same analogues which were required to produce negative inotropic and antiarrythmic effects (ED40) on isolated rabbit atria [D. O. Rauls and J. K. Baker, J. med. Chem, 22, 81 (1979)]. These effects showed correlations of 0.945 and 0.936, respectively, with the 22Na+ uptake inhibition. It is concluded from this information that a substantial proportion of the negative inotropic and antiarrythmic effects of propranolol is due to its action on sodium channels.