11-OXO-TETRODOTOXIN AND A SPECIFICALLY LABELED H-3 TETRODOTOXIN

Tetrodotoxin was oxidized to a hydrated aldehyde, 11-oxo-tetrodotoxin, which shares the specificity of tetrodotoxin for the Na+ channel of t he isolated voltage-clamped frog skeletal muscle fiber, but is four to five times more potent. It binds to the solubilized Na+ channel of ee l electroplax with a similarly higher potency, because of an equilibri um dissociation constant about 0.25, and a dissociation rate constant 2.4 times slower than those for tetrodotoxin. 11-Oxo-tetrodotoxin can be reduced to regenerate a tetrodotoxin, which is chemically and biolo gically indistinguishable from the original tetrodotoxin. By reducing with tritiated sodium borohydride, a H-3 marker can be inserted regios pecifically to yield 11-[H-3]-tetrodotoxin. Because it has a defined s pecific activity of >2.5 Ci/mmole, and a H-3 marker which does not exc hange with solvent proton, 11-[H-3]-tetrodotoxin is an ideal tracer fo r tetrodotoxin. It may enable studies of problems which require higher signals and/or better stability of the marker than those obtainable f rom currently available tracer Na+-channel ligands. (C) 1996 Elsevier Science Ltd.