Dinoflagellates from marine algal blooms produce neurotoxic compounds: effects on free calcium levels in neuronal cells and synaptosomes

In this report, evidence is presented that the marine unicellular eukaryoti c dinoflagellates can cause neurotoxicity very likely by an increase in int racellular free calcium ions ([Ca2+](i)). Determinations of the effects of culture supernatants from different clones of the dinoflagellate Alexandriu m sp. isolated from algal blooms on the viability of rat primary neuronal c ells revealed that all clones tested were toxic for these cells. In additio n, all Alexandrium clones tested, except for A. ostenfeldii BAH ME-141, wer e found to be toxic for rat pheochromocytoma PC12 cells. No toxicity was ob served for culture supernatants from Gonyaulax and Coolia monotis. Calcium ions are important in the process of apoptotic cell death; our studies reve aled that the dinoflagellate supernatants from A. lusitanicum K2, A. lusita nicum BAH ME-091, and A. tamarense 1M caused an increase in [Ca2+](i) level s in both PC12 cells and primary neuronal cells. These dinoflagellate super natants, as well as the A. tamarense ccmp 115 supernatant, were found to ca use also an increase in free calcium concentration in isolated synaptosomes . Our results suggest that the neurotoxic effects of certain dinoflagellate supernatants may be associated with disturbances in [Ca2+](i) levels. (C) 2000 Elsevier Science B.V. All rights reserved.