A toxic extract of the marine phytoflagellate Prymnesium parvum induces calcium-dependent release of glutamate from rat brain synaptosomes

Blooms of the marine phytoflagellate Prymnesium parvum produced mass mortality of fish in Norway and many other parts of the world. The effects of a purified algae extract of P. parvum on transmitter release from rat brain synaptosomes were studied to characterize its toxic action. Synaptosomes are detached nerve terminals and represent a simple system that has retained the machinery for uptake, synthesis, storage, and release of neurotransmitters. A crude methanol extract of P. parvum was purified by reverse-phase column for fast protein liquid chromatography (FPLC). The purified extract stimulated Ca(2+)-dependent spontaneous release of glutamate in a concentration-dependent manner. The release was increased by addition of extracellular Ca(2+). The release of glutamate was suppressed by the Ca(2+)-channel blockers; flunarizine (10 muM), diltiazem (10 muM), and verapamil (10 muM). The stimulation of release of glutamate from rat brain synaptosomes induced by the toxin may be due to an ionophorelike property of the algae extract such as previously reported for the potent algal toxin maitotoxin. At high concentrations the toxin primarily acts as a powerful lytic agent.