Characterisation of marrubenol, a diterpene extracted from Marrubium vulgare , as an L‐type calcium channel blocker

The objective of the present study was to investigate the mechanism of the relaxant activity of marrubenol, a diterpenoid extracted from Marrubium vulgare . In rat aorta, marrubenol was a more potent inhibitor of the contraction evoked by 100 m M KCl (IC 50 : 11.8±0.3 μ M , maximum relaxation: 93±0.6%) than of the contraction evoked by noradrenaline (maximum relaxation: 30±1.5%). In fura‐2‐loaded aorta, marrubenol simultaneously inhibited the Ca 2+ signal and the contraction evoked by 100 m M KCl, and decreased the quenching rate of fura‐2 fluorescence by Mn 2+ . Patch‐clamp data obtained in aortic smooth muscle cells (A7r5) indicated that marrubenol inhibited Ba 2+ inward current in a voltage‐dependent manner ( K D : 8±2 and 40±6 μ M at holding potentials of −50 and −100 mV, respectively). These results showed that marrubenol inhibits smooth muscle contraction by blocking L‐type calcium channels.British Journal of Pharmacology (2003) 140 , 1211–1216. doi: 10.1038/sj.bjp.0705561