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Inhibition of Maitotoxin‐Induced Ca 2+ Influx in Rat Glioma C6 Cells by Brevetoxins and Synthetic Fragments of Maitotoxin
Author(s) -
Konoki Keiichi,
Hashimoto Masaki,
omura Taro,
Sasaki Makoto,
Murata Michio,
Tachibana Kazuo
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.70010409.x
Subject(s) - tetrodotoxin , melittin , chemistry , sodium channel , marine toxin , stereochemistry , depolarization , pharmacology , sodium , peptide , toxin , biophysics , biochemistry , biology , organic chemistry
45 Ca 2+ influx in rat glioma C6 cells induced by 0.3 n M maitotoxin (MTX) was markedly inhibited by brevetoxin A (PbTx1) and brevetoxin B (PbTx2), with EC 50 values of 16 and 13 µ M , respectively. This inhibition was observed immediately after addition of MTX when monitored with fura‐2, which suggests that PbTx2 directly blocks the action of MTX. This blockade by PbTx2 was not affected by tetrodotoxin, which excludes the involvement of voltage‐sensitive sodium channels. The depolarizing effects of these brevetoxins were also not a likely cause of this inhibition, because melittin, a channel‐forming peptide, did not significantly block MTX‐induced 45 Ca 2+ influx. Instead, this inhibition was thought to be mediated by blockade of an MTX‐binding site by the brevetoxins, based on the fact that these toxins, particularly PbTx2, closely mimic the partial structure of MTX. Synthetic fragments of MTX corresponding to the hydrophilic EF‐GH rings (200 µ M ) and LM‐NO rings (500 µ M ) of MTX significantly reduced MTX‐elicited Ca 2+ influx. The observation that the effects of MTX were inhibited by structural mimics of both its hydrophobic and hydrophilic portions implies that both portions of the MTX molecule recognize its target.