Molecular mechanisms of vasoselectivity of the 1,4‐dihydropyridine lercanidipine

The effects of (S)‐ and (R)‐lercanidipine on CHO cells stably expressing the cardiac (Ca v 1.2a) or vascular (Ca v 1.2b) splice variant of the L‐type calcium channel pore subunit were studied, using whole‐cell and single‐channel patch‐clamp measurements. Lercanidipine block of Ca v 1.2b current was enantioselective. (S)‐lercanidipine was 4.1‐fold more potent. Experiments using acidic solutions (pH 6.8) revealed a 6.4‐fold enhanced inhibitory effect of (S)‐lercanidipine compared with physiological conditions (pH 7.4) indicating that the charged form mediates inhibition. At depolarised holding potential (−40 mV), (S)‐lercanidipine exhibited a 35‐fold greater potency, compared with standard conditions (−80 mV). A comparison of the concentration‐dependent inhibition of Ca v 1.2a with Ca v 1.2b subunit currents by (S)‐lercanidipine revealed only a 1.8‐fold difference in IC 50 , but the slope of the dose–response curve was much steeper ( n H =2.3) with Ca v 1.2a, compared with Ca v 1.2b ( n H =0.8). This indicates overlap between agonistic and antagonistic effects, predominant with the cardiac Ca v 1.2a subunit. This idea is supported by transient stimulatory effects, and a slight leftward shift of the IV curves. These effects were more prominent for Ca v 1.2a than for Ca v 1.2b. Single‐channel experiments confirmed typical features of calcium channel agonists such as prolonged channel openings, a component of lengthened openings, and an enhanced open probability in the presence of (S)‐lercanidipine. Again, these findings were concentration‐dependent and more pronounced for Ca v 1.2a than for Ca v 1.2b. Our data indicate a splice‐variant predominant agonism as a new mechanism contributing to the vasoselectivity of lercanidipine, along with marked voltage‐dependence of action.British Journal of Pharmacology (2004) 142 , 275–284. doi: 10.1038/sj.bjp.0705786