in the presence of verapamil or methoxyverapamil ( d 600 ) the tonic contraction , but not the phasic contraction , could be evoked by a single strong stimulus , while in the presence of sodium nitroprusside the phasic contraction , but not the tonic contraction , could be provoked by a single strong stimulus .
C0042523
verapamil
C0016986
methoxyverapamil