J. Biol. Chem., Vol. 260, Issue 6, 3431-3439, Mar, 1985
Functional unit size of the neurotoxin receptors on the voltage- dependent sodium channel
KJ Angelides, TJ Nutter, LW Elmer and ES Kempner
Radiation inactivation was used in situ to determine the functional unit
sizes of the neurotoxin receptors of the voltage-dependent sodium channel
from rat brain. Frozen or lyophilized synaptosomes were irradiated with
high energy electrons generated by a linear accelerator and assayed for
[3H]saxitoxin, 125I-Leiurus quinquestriatus quinquestriatus (alpha-scorpion
toxin), 125I-Centruroides suffusus suffusus (beta-scorpion toxin), and
batrachotoxinin-A 20 alpha- [3H]benzoate binding activity. The functional
unit size of the neurotoxin receptors determined in situ by target analysis
are 220,000 for saxitoxin, 263,000 for alpha-scorpion toxin, and 45,000 for
beta- scorpion toxin. Analysis of the inactivation curve for
batrachotoxinin- A 20 alpha-benzoate binding to the channel yields two
target sizes of Mr approximately 287,000 (50%) and approximately 51,000
(50%). The results are independent of the purity of the membrane
preparation. Comparison of the radiation inactivation data with the protein
composition of the rat brain sodium channel indicates that there are at
least two functional components.
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