Novel dihydropyridines with positive inotropic action through activation of Ca2+ channels

Transmembrane influx of extracellular calcium through specific calcium channels is now accepted to have an important role in the excitation-contraction coupling of cardiac and smooth muscle. The importance of such slow calcium channels has been underlined by the development of specific calcium channel blocking agents, the 'calcium antagonists', typified by verapamil, nifedipine and diltiazem. These drugs have been used to investigate the properties of slow calcium channels in a variety of tissues. We have found that small modifications to the nifedipine molecule produce other dihydropyridine derivatives (see Fig. 1) with effects diametrically opposite to those of the calcium antagonists: cardiac contractility is stimulated and smooth muscle is contracted. These effects are competitively antagonized by nifedipine. Apparently, nifedipine and the novel compounds bind to the same specific dihydropyridine binding sites in or near the calcium channel. In contrast to nifedipine, however, the new compounds promote--instead of inhibiting--the influx of Ca2+ ions. We report here the properties of BAY K 8644 (methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)- pyridine-5-carboxylate), one of the most potent of these novel compounds.