Effects of VA-045, a novel apovincaminic acid derivative, on rabbit basilar artery

We investigated the effects of VA-045, an apovincaminic acid derivative, on isolated basilar artery of the rabbit. In basilar artery precontracted with histamine (10(-6) M), VA-045 (10(-9) to 10(-5) M) produced a concentration-dependent relaxation, but VA-045-induced relaxation was significantly reduced when the tonus of the mesentery was raised by isotonic high K+ (30 or 65 mM) or histamine (10(-6) M) with 15 mM K+. VA-045-induced relaxations of the basilar artery were not affected by 10 mM tetraethylammonium (TEA), 10(-6) M 4-aminopyridine, 10(-6) M charybdotoxin, 10(-7) M apamin and 10(-6) M glybenclamide. VA-045-induced relaxation was not influenced by 10(-5) M methylene blue. These results suggest that increased open probability of potassium channels, which are not Ca(2+)-dependent K(+)-channels or TEA- or ATP-sensitive K(+)-channels, may be involved in VA-045-induced relaxation of basilar artery.