Differential properties of the optical‐isomers of pranidipine, a 1,4‐dihydropyridine calcium channel modulator

Pranidipine is an optically-active 1,4-dihydropyridine (DHP) voltage-dependent L-type calcium channel inhibitor. Certain enantiomeric pairs display opposite effects, i.e., inhibition and activation of the calcium channel while others exhibit the same qualitative actions. We investigated pranidipine, a new DHP, using a paradigm of vascular smooth muscle reactivity. In isolated rat aorta, depolarized with 80 mM KCI, both isomers of pranidipine caused a right-ward shift of the concentration-contraction curves for extracellular Ca 2 + . The apparent pA 2 values of the S-isomer and R-isomer were 10.03 and 8.36, respectively, providing evidence that the calcium channel blocking action of the S-isomer was 50 times more potent than that of the R-isomer. Antihypertensive actions of these two isomers studied in pentobarbital-anaesthetized spontaneously hypertensive rats, revealed that the S-isomer, at doses of 3-30 μg/kg i.v. decreased blood pressure in a dose-dependent manner, while the R-isomer had no effect on blood pressure at those doses. We conclude that the pair of enantiomers of pranidipine qualitatively display the same Ca 2+ channel blocking action and that neither isomer exhibits Bay K 8644-like activation. PranidiDine mav be useful in studies on the architecture of the DHP receptor 'pocket'.