Mechanism of the action of angiotensin-converting enzyme inhibitors on agonist-induced Ca2+ influx.

To evaluate the direct effects of the angiotensin-converting enzyme (ACE) inhibitors, captopril, enalaprilat, enalapril (a prodrug without therapeutically significant ACE inhibitory effect) and ramiprilat, on cellular calcium metabolism, the cytosolic free calcium concentration was measured in cultured rat vascular smooth muscle cells using the fluorescent dye, fura-2. Preincubation with captopril, enalaprilat, enalapril, or ramiprilat for 40 min significantly reduced the angiotensin II-induced transplasma membrane calcium influx but did not influence the angiotension II-induced calcium release from internal stores. Captopril and ramiprilat also inhibited arginine vasopressin, but not the thapsigargin-, norepinephrine-, or the BayK 8644-induced changes in cytosolic calcium. Phorbol 12-myristate 13-acetate pretreatment for 30 s caused an increase in the angiotensin II-induced rise in cytosolic calcium. Although both captopril and verapamil reduced responses to angiotensin II to similar extents, only verapamil blocked the ability of phorbol 12-myristate 13-acetate to enhance responses to angiotensin II. It is concluded that ACE inhibitors modulate the effects of some but not all agonist-induced transplasma membrane calcium influx.