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 Ca2+ 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, Ca2+ movements and ERK 1/2 activation were studied by measurement of the intracellular Ca2+ 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 Ca2+ mobilization (i.e. Ca2+ release from internal stores); these dihydropyridines did not affect either Ca2+ influx or ERK 1/2 activation. In bFGF-stimulated SMCs, amlodipine and isradipine reduced both Ca2+ influx and ERK 1/2 activation without affecting Ca2+ 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 Ca2+ 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 Ca2+ mobilization, likely by interacting with the sarcoplasmic reticulum and (ii) inhibit voltage-dependent Ca2+ 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.