GAMBIERTOXIN (CTX-4B), PURIFIED FROM WILD GAMBIERDISCUS-TOXICUS DINOFLAGELLATES, INDUCES NA-DEPENDENT SWELLING OF SINGLE FROG MYELINATED AXONS AND MOTOR-NERVE TERMINALS IN-SITU()

The effects of gambiertoxin (CTX-4B), purified from the dinoflagellate Gambierdiscus toxicus, were assessed on the morphology of both frog m yelinated axons and motor nerve terminals, using confocal laser scanni ng microscopy. During the action of the toxin (24 and 30 nM), a marked swelling of nodes of Ranvier and motor nerve terminals was observed. The CTX-4B-induced swelling could be prevented by blocking voltage-dep endent Na+ channels with tetrodotoxin, and could be partly reversed by an external hyperosmotic solution containing 100 mM D-mannitol. The r esults suggest that CTX-4B, by modifying voltage-dependent Nai channel s, increases internal Na+ concentration of axons and nerve terminals a nd consequently induces water influx to compensate such an increase. I t is suggested that stimulated transmitter release by CTX-4B, as well as by hyperosmotic d-mannitol, contribute also to the swelling of the terminals through an increase in their surface area. (C) 1997 Elsevier Science Ireland Ltd.