Dual mechanism of action of amlodipine in human vascular smooth muscle cells

OBJECTIVES It has been recently shown that calcium channel blockers (CCBs) could also control smooth muscle cell (SMC) growth/reactivity through mechanisms that were unrelated to their CCB property. Here, we investigated the effects of amlodipine and isradipine on Ca movements and p42/p44 mitogen-activated protein kinase (ERK 1/2) activities, which are two early signalling events triggered by growth factors such as thrombin and basic fibroblast growth factor (bFGF). METHODS In cultured human SMCs isolated from internal mammary arteries, Ca movements and ERK 1/2 activation were studied by measurement of the intracellular Ca concentration in Fura 2-labelled SMCs and by Western blots, respectively. RESULTS In thrombin- and thapsigargin-stimulated SMCs, amlodipine and not isradipine dose-dependently reduced Ca mobilization (i.e. Ca release from internal stores); these dihydropyridines did not affect either Ca influx or ERK 1/2 activation. In bFGF-stimulated SMCs, amlodipine and isradipine reduced both Ca influx and ERK 1/2 activation without affecting Ca mobilization. ERK 1/2 activation could also be directly stimulated by the l-type channel agonist Bay K 8644, demonstrating the involvement of voltage-gated Ca influx in this process. Most of the observed effects described were obtained with approximately 10 nmol/l amlodipine/isradipine (i.e. concentrations close to the peak plasma level in treated patients). CONCLUSIONS In human SMCs, amlodipine can (i) specifically alter Ca mobilization, likely by interacting with the sarcoplasmic reticulum and (ii) inhibit voltage-dependent Ca influx and the resulting ERK 1/2 activation. It is likely that amlodipine exerts its growth-inhibitory potency by interfering with multiple branches of mitogenic signalling pathways.