[Electromechanical uncoupling of vascular smooth muscle as the basic principle of coronary dilatation by 4-(2'-nitrophenyl-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid dimethyl ester (BAY a 1040, Nifedipine). 1. The significance of Ca ++ ions for the bioelectrical and mechanical activity of smooth muscle].