Dual action of d-cis-diltiazem on calcium entry in guinea-pig papillary muscle cells

Previous studies have shown that the ability of calcium antagonists to inhibit the contraction of heart muscle was strongly dependent on the enantiomeric configuration of these drugs. The authors have now compared the electrophysiological effects of the stereo-isomers and the racemic mixture of cis-diltiazem on isolated guinea-pig papillary muscle. The results show that l-cis-diltiazem did not possess calcium entry blocking properties up to a concentration of 10 mu mol/1. Surprisingly the d-enantiomer showed, at low concentrations, a statistically significant increase of the area of the slow response.