Effects of SAS 1310, a new calcium antagonist, on isolated myocardial and smooth muscle preparations.

Some features of the effects of the diltiazem derivative SAS 1310 on in vitro myocardial and smooth muscle preparations were compared to those of the effects of diltiazem. Left atria, aortic strips and taenia coli of guinea-pigs were used. SAS 1310 induced a negative inotropic response of the left atria driven at 1 Hz similar to the response to diltiazem (IC50 values: SAS 1310 1.34 microM, diltiazem 0.8 microM). The inotropic effect of diltiazem (5 microM) was clearly rate-dependent whereas the reduction of left atria contractility induced by SAS 1310 (5 microM) was not modified by changes of the stimulation rate (the range of frequencies used was 0.5-2 Hz, with stepwise changes of 0.5 Hz). Diltiazem (0.1-0.5 microM) was more effective than SAS 1310 (0.1-5 microM) in inhibiting the contractile response to calcium of taenia coli depolarized by high K+ as well as in relaxing the aortic strips contracted by high K+ (IC50 SAS 1310 12.3 microM, diltiazem 0.41 microM). The response of aortic strips to norepinephrine (50 microM) in Ca2+-free medium was inhibited by SAS 1310 (50 microM) and was not affected by diltiazem (2 microM). The drug concentrations used were equiactive in inhibiting the high K+-induced contraction of the aortic strips. The different effects of diltiazem and its derivative on left atria contraction at different force-frequency ratios and on aortic strip contraction induced by norepinephrine in a Ca2+-free medium suggest that the actions of the two drugs differ qualitatively.