KAPPA-FLAVITOXIN - ISOLATION OF A NEW NEURONAL NICOTINIC RECEPTOR ANTAGONIST THAT IS STRUCTURALLY RELATED TO KAPPA-BUNGAROTOXIN

A peptide, termed kappa-flavitoxin (.kappa.-flavitoxin), has been purified from the venom of the red-headed krait, Bungarus flaviceps, by low- and high-pressure liquid chromatography. .kappa.-Flavitoxin has a pI of 8.8 and an apparent molecular weight on sodium dodecyl-sulfate-polyacrylamide gel electrophoresis of 6500 Da. .kappa.-Flavitoxin is a potent inhibitor of nicotinic transmission in autonomic ganglia, producing a complete and long-lasting blockade at doses as low as 50 nM. Intracellular recordings reveal a selective blockade of neuronal nicotinic receptors by the toxin, with no effects on other active or passive properties of neuronal membranes. .kappa.-Flavitoxin shares a number of pharmacological and biochemical properties with .kappa.-bungarotoxin, purified from the venom of Bungarus multicinctus. The two peptides exhibit considerable homology in their amino acid sequences. Radiolabeled .kappa.-flavitoxin binds to a nicotine site in ciliary ganglia previously identified by .kappa.-bungarotoxin, which appears to be associated with the neuronal nicotinic receptor. This site is not recognized by .alpha.-bungarotoxin, which also does not block nicotinic transmission in this ganglion.