title: The vaso-contractile action of zooxanthellatoxin-B from a marine dinoflagellate is mediated via Ca2+ influx in the rabbit aorta.
abstract: We previously showed that zooxanthellatoxin-B, isolated from dinoflagellate, caused a sustained contraction of the aorta in an external Ca2+-dependent manner. To clarify the role of Ca2+ in this action, we examined the effects of zooxanthellatoxin-B as well as a depolarizing stimulus (60 mM KCl), using the simultaneous recording for cytosolic Ca2+ level (fura-2) and developed tension in the rabbit aorta. KCl (60 mM) elicited a rapid cytosolic Ca2+ elevation followed by a pronounced contraction, and time required for half-maximum contraction was 2 min. Zooxanthellatoxin-B caused an increase in cytosolic Ca2+ followed by a gradual contraction, with a time for half-maximum contraction of 5-10 min in a concentration-dependent manner. We found a strong correlation between Ca2+ elevation and the contraction in zooxanthellatoxin-B action. In a Ca2+-free solution, zooxanthellatoxin-B caused neither the contraction nor the increase in cytosolic Ca2+. Furthermore, both pre- and post-treatment with verapamil, a voltage-operated Ca2+-channel blocker, partially suppressed both an increase in cytosolic Ca2+ and the contraction by zooxanthellatoxin-B. Zooxanthellatoxin-B-induced contraction was also inhibited by other voltage-operated Ca2+-channel blockers: nifedipine or diltiazem. These results suggest that zooxanthellatoxin-B-elicited contraction is caused by a Ca2+ influx into the smooth muscle cells, partially via voltage-operated Ca2+ channels.
authors.affiliation: Department of Pharmaceutical Molecular Biology, Pharmaceutical Institute, Tohoku University, Sendai, Miyagi, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Moriya
authors.forename: K
authors.initials: K
authors.lastname: Furukawa
authors.forename: H
authors.initials: H
authors.lastname: Nakamura
authors.forename: A
authors.initials: A
authors.lastname: Murai
authors.forename: Y
authors.initials: Y
authors.lastname: Ohizumi
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D056890:Eukaryota / Q000737:chemistry*; D066298:In Vitro Techniques; D008297:Male; D008387:Marine Toxins / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D011090:Polyenes / Q000494:pharmacology*; D011817:Rabbits; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D008387:Marine Toxins; D011090:Polyenes; D014662:Vasoconstrictor Agents; C081401:zooxanthellatoxin B; D002118:Calcium