Pharmacologic properties of a novel Ca2+ entry blocker, AJ-2615, in vitro

We studied the in vitro vascular relaxant properties of AJ-2615, (+/-)-N-[6,11-dihydrodibenzo[b,e]-thiepin-11-yl]-4-[4- fluorophenyl]-1-piperazinebutanamide monomaleate, a novel compound with long-lasting antihypertensive activity. AJ-2615 inhibited the high K(+)-induced contractile response in rat aorta with an IC50 of 2.08 x 10(-8) M. It was 13 times less potent than nifedipine and 3, 10, and 15 times more potent than verapamil, diltiazem, and fluanarizine, respectively. AJ-2615 also inhibited the high K(+)-induced 45Ca influx in rat aorta at almost the same concentration as that for inhibition of the contractile response. The inhibition of 45Ca influx was reversed by Bay k 8644, a Ca2+ channel agonist. The effects of AJ-2615 on the contractile response and Ca2+ influx persisted for at least 120 min after AJ-2615 was removed from the medium. These results indicate that AJ-2615 acts directly on the potential-dependent Ca2+ channel in a long-lasting manner. AJ-2615 inhibited [3H]prazosin binding to dog aortic membranes (IC50 = 1.25 x 10(-8) M) and phenylephrine-induced contractile response in superior mesenteric artery (SMA) of rabbits (IC50 = 3.87 x 10(-8) M), indicating that AJ-2615 has potent alpha 1-adrenoceptor blocking activity. AJ-2615 at 10(-6) M did not inhibit the caffeine-induced contractile response in rabbit SMA in Ca(2+)-free medium, nor did it inhibit calmodulin (CAM) activity.(ABSTRACT TRUNCATED AT 250 WORDS)