ROLE OF L-TYPE CALCIUM CHANNELS ON STIMULATED CALCIUM INFLUX AND ON PROLIFERATIVE ACTIVITY OF HUMAN CORONARY SMOOTH-MUSCLE CELLS

Dihydropyridine (DHP) calcium channel blockers are widely used in treatment of coronary artery disease. To evaluate the specific role of L-type calcium channels in the antianginal and possibly antiatherosclerotic properties of DHP inhibitors, we examined the effects of a 1,4-DHP agonist and antagonist on angiotensin II (ANG II)- and serum-stimulated calcium influx and proliferation of human coronary smooth muscle cells (cSMC). Fluorometry of fura-2 was used to measure changes in free cytosolic Ca2+ concentration ([Ca2+](i)) in cSMC after short- and long-term pretreatment with the calcium agonist Bay K 8644 or the antagonist nitrendipine, respectively. Proliferative activity was quantified during exponential growth in serum-supplemented medium with or without both DHPs. Short- and long-term pretreatment with Bay K 8644 increased basal [Ca2+](i) significantly in resting cells and augmented ANG II- and serum-induced sustained [Ca2+](i) responses. Concordantly, proliferation rate was increased. In contrast, nitrendipine had no significant effect on basal or stimulated [Ca2+](i) after short-term treatment, but decreased [Ca2+](i) after 24-h incubation, attenuated the plateau phase of ANG II- and serum-evoked [Ca2+](i) transients, and reduced proliferative activity of these cells. The results indicate that 1,4-DHPs modulate ANG II- and serum-induced Ca2+ influx in cSMC. Thus, L-type calcium channels may contribute to [Ca2+](i) transients evoked by ANG II and serum. Moreover, the modulating effects of both DHPs on proliferative activity suggest involvement of DHP-sensitive calcium channels. Calcium influx through L-type channels may be one of the mechanisms that determine responsiveness to vasoconstrictors and proliferative activity of human cSMC.