US EPA

2775748 

Journal Article 

Binding of batrachotoxinin A 20-alpha-benzoate to a receptor site associated with sodium channels in synaptic nerve ending particles 

Catterall, WA; Morrow, CS; Daly, JW; Brown, GB 

1981 

Yes 

Journal of Biological Chemistry
ISSN: 0021-9258
EISSN: 1083-351X 

HEEP/82/06202 

256 

17 

8922-8927 

6114956 

WOS:A1981MF70800016 

HEEP COPYRIGHT: BIOL ABS. Specific binding of (3H)batrachotoxinin A 20-alpha-benzoate to Na channels in rat brain synaptosomes was studied. Specific binding is increased 10- to 20-fold by the polypeptide scorpion toxin which binds at a different receptor site on the Na channel. The K0.5 for enhancement of (3H)batrachotoxinin A 20-alpha-benzoate binding by scorpion toxin is 35 nM in medium containing 5 mM K+. Depolarization of synaptosomes with 135 mM K+ increases K0.5 to 300 nM. The Kd for scorpion toxin binding to its receptor site is closely correlated with K0.5 for enhancement of binding of (3H)batrachotoxinin A 20-alpha-benzoate at both membrane potentials. Sea anemone toxin II has the same effect as scorpion toxin at 200-fold higher concentration. In the presence of scorpion toxin the alkaloids batrachotoxin, veratridine and aconitine block binding of (3H)batrachotoxinin A 20-alpha-benzoate with Kd values of 0.05, 7 and 1.2 muM, respectively. These Kd values are closely correlated with values of K0.5 for activation of Na channels by these alkaloid toxins. Scatchard analysis of binding of (3H)batrachotoxinin A-20-alpha-benzoate binding in the presence of 1 muM scorpion toxin indicates a single class of sites with a Kd of 82 nM and a binding capacity of 2.1 | 0.2 pmol/mg of protein. At lower scorpion toxin concentrations, Kd is increased with no change in binding capacity. Results demonstrate the value of (3H)batrachotoxinin A 20-alpha-benzoate as a binding probe of the alkaloid neurotoxin receptor site on the Na channel and provide direct confirmation of the allosteric mechanism of toxin binding and action at this site.