Abstract:
:The anticonvulsants phenytoin and carbamazepine interact allosterically with the batrachotoxin binding site of sodium channels. In the present study, we demonstrate an autoradiographic technique to localize the batrachotoxin binding site on sodium channels in rat brain using [3H]batrachotoxinin-A 20-alpha-benzoate (BTX-B). Binding of [3H]BTX-B to brain sections is dependent on potentiating allosteric interactions with scorpion venom and is displaced by BTX-B (Kd approximately 200 nM), aconitine, veratridine, and phenytoin with the same rank order of potencies as described in brain synaptosomes. The maximum number of [3H]BTX-B binding sites in forebrain sections (approximately 1 pmol/mg of protein) also agrees with biochemical determinations. Autoradiographic localizations indicate that [3H]BTX-B binding sites are not restricted to cell bodies and axons but are present in synaptic zones throughout the brain. For example, a particularly dense concentration of these sites in the substantia nigra is associated with afferent terminals of the striatonigral projection. By contrast, myelinated structures possess much lower densities of binding sites. In addition, we present electrophysiological evidence that synaptic transmission, as opposed to axonal conduction, is preferentially sensitive to the action of aconitine and veratridine. Finally, the synaptic block produced by these sodium channel activators is inhibited by phenytoin and carbamazepine at therapeutic anticonvulsant concentrations. Thus, these anticonvulsants may limit seizure spread not only by affecting all-or-none conduction by axonal sodium channels but also by modulating graded aspects of synaptic transmission.
journal_name
Proc Natl Acad Sci U S Aauthors
Worley PF,Baraban JMdoi
10.1073/pnas.84.9.3051subject
Has Abstractpub_date
1987-05-01 00:00:00pages
3051-5issue
9eissn
0027-8424issn
1091-6490journal_volume
84pub_type
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