Electrophysiological evaluation of the beta-blocking properties and direct membrane effects of l-moprolol and its enantiomer d-moprolol.

The electrophysiological and beta-blocking properties of l- and d-moprolol have been studied in sheep cardiac Purkinje fibers. l-Moprolol (0.3-100 nM) dose-dependently antagonized the inotropic (ED50 = 1.2 +/- 0.4 nM) and chronotropic (ED50 = 5.8 +/- 0.6 nM) effects of isoprenaline. d-Moprolol (0.3-100 nM) was fully devoid of beta-blocking properties under the same experimental conditions. Both isomers had the same electrophysiological profile: they did not influence action potential characteristics, contractility and normal automaticity up to 1 microM. On the whole, l-moprolol appears to be a potent beta-blocker, exerting membrane depressant effects only at a concentration 2000 times higher than those exerting effective beta-blockade.