title: Azaspiracid-4 inhibits Ca2+ entry by stored operated channels in human T lymphocytes.
abstract: Azaspiracids (AZs) are a new group of phycotoxins discovered in the Ireland coast that includes the isolated analogues: AZ-1, AZ-2, AZ-3, AZ-4 and AZ-5 and the recently described AZ-6-11. Azaspiracid toxic episodes show gastrointestinal illness, but neurotoxic symptoms are also observed in mouse bioassay. Despite their great importance in human health, so far its mechanism of action is largely unknown. In this report, we present the first data about the effect of AZ-4 on cytosolic calcium concentration [Ca2+]i in freshly human lymphocytes. Cytosolic Ca2+ variations were determined by fluorescence digital imaging microscopy using Fura2 acetoxymethyl ester (Fura2-AM). AZ-4 did not modify cytosolic Ca2+ in resting cells. However, the toxin dose-dependent inhibited the increase in cytosolic Ca2+ levels induced by thapsigargin (Tg). AZ-4 decreased Ca2+-influx induced by Tg but did not affect the Ca2+-release from internal stores induced by this drug. The effects of AZ-4 on Ca2+-influx induced by Tg were reversible and not regulated by adenosine 3',5'-cyclic monophosphate (cAMP) pathway. When AZ-4 was added before, after or together with nickel, an unspecific blocker of Ca2+ channels, the effects were indistinguishable and additive. AZ-4 also inhibited maitotoxin (MTX)-stimulated Ca2+-influx by 5-10%. Thus, AZ-4 appeared to be a novel inhibitor of plasma membrane Ca2+ channels, affecting at least to store operated channels, showing an effect clearly different from other azaspiracid analogues.
authors.affiliation: Departamento de Farmacología, Facultad de Veterinaria, USC, 27002 Lugo, Spain.
authors.forename: Amparo
authors.initials: A
authors.lastname: Alfonso
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Román
authors.forename: Mercedes R
authors.initials: MR
authors.lastname: Vieytes
authors.forename: Katsuya
authors.initials: K
authors.lastname: Ofuji
authors.forename: Masayuki
authors.initials: M
authors.lastname: Satake
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yasumoto
authors.forename: Luis M
authors.initials: LM
authors.lastname: Botana
mesh_terms: D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008387:Marine Toxins / Q000737:chemistry / Q000494:pharmacology*; D013141:Spiro Compounds / Q000737:chemistry / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism*; D000095702:Polyether Toxins
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008387:Marine Toxins; D013141:Spiro Compounds; C406592:azaspiracid; D000095702:Polyether Toxins