Abstract
Binding of [125I]α-bungarotoxin to acetylcholine receptors of ganglionic homogenate of the marine mollusc Aplysia is blocked by the anticholinesterases eserine (I50 = 4 µM) and neostigmine (I50 = 0.2 mM). The classical acetylcholine antagonist d-tubocurarine blocks with an I50 of 2 µM. Eserine (I50 = 3.2 µM) and neostigmine (I50 > 1 mM) also block toxin binding to a solubilized receptor preparation. In contrast to their relative potency in blocking toxin binding, neostigmine is a more potent inhibitor of Aplysia acetylcholinesterase (I50 = 14 nM) than is eserine (I50 = 250 nM). α-Bungarotoxin does not affect esterase activity or interfere with the ability of eserine to block the esterase. The response to acetylcholine recorded through intracellular microelectrodes is blocked by α-bungarotoxin. Neither eserine nor neostigmine blocks the acetylcholine response; rather, they prolong and increase it, as expected from their effects on the esterase. Eserine (0.1 mM) blocks the α-bungarotoxin inhibition of the physiological acetylcholine response. These results indicate that eserine and neostigmine block the binding of α-bungarotoxin by interacting with a site which is different from both the esterase and the cholinergic sites of the acetylcholine receptor.
- Copyright © 1976 by Academic Press, Inc.
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