VASOCONSTRICTION INDUCED BY ZOOXANTHELLATOXIN-B, A POLYOXYGENATED LONG-CHAIN PRODUCT FROM A MARINE ALGA

We found that zooxanthellatoxin-B from a symbiotic marine alga. Symbio dinium sp., caused a concentration-dependent contraction of the rabbit isolated aorta at concentrations of 10(-7)-10(-5) M. Verapamil (10(-6 ) M) and mefenamic acid (10(-5) M) significantly attenuated the contra ctile response to zooxanthellatoxin-B at lower concentrations (10(-7)- 10(-6) M) but not at higher concentrations (3 x 10(-6) 10(-5) M). The response to zooxanthellatoxin-B was partly inhibited by phentolamine ( 10(-6) M), whereas it was potentiated by ouabain (10(-5) M). Tetrodoto xin (10(-6) M), methysergide (10(-6) M), chlorpheniramine (10(-6) M) o r indomethacin (3 x 10(-6) M), however, did not affect it. The zooxant hellatoxin-B-induced contraction was abolished by incubation in Ca2+-f ree solution. The contractile response increased in a concentration-de pendent fashion with Ca2+ (0.03 and 10 mM) or Sr2+ (0.10 and 10 mM). A fter treatment with verapamil (10(-6) or 5 x 10(-6) M), the concentrat ion-contractile response curves for Ca2+ and Sr2+ in the presence of z ooxanthellatoxin-B were shifted to the right in parallel. MgCl2 (10 mM ) shifted the concentration-response curve for Ca2+ more markedly than did verapamil. Zooxanthellatoxin-B increased tissue Na+ and reduced t issue K+ contents in the aorta, suggesting that zooxanthellatoxin-B in creases Na+ and K+ permeability across the plasma membrane. These resu lts suggest that the zooxanthellatoxin-B-induced contraction of the ao rta is caused mainly by a direct action on smooth muscle, i.e., an inc rease in Ca2+ permeability that occurs at least partly through voltage -sensitive Ca2+ channels as well as through nonselective cation channe ls in the cell membrane of smooth muscle. (C) 1998 Elsevier Science B. V. All rights reserved.