0000000000248850
AUTHOR
Christoph Methfessel
Noncompetitive agonism at nicotinic acetylcholine receptors; functional significance for CNS signal transduction.
The alkaloids (-)physostigmine (Phy), galanthamine (Gal) and codeine (Cod), and several derivatives and homologous compounds, can act as noncompetitive agonists (NCA) of nicotinic acetylcholine receptors (nAChR) from Torpedo electrocytes, frog and mammalian muscle cells, clonal rat pheochromocytoma cells, cultured hippocampal neurons and several ectopic expression systems, by interacting with a binding site on the alpha-subunits of these nAChRs that is insensitive to the natural transmitter, acetylcholine (ACh), and ACh-competitive agonists and antagonists. Several endogenous ligands, including opioid-type compounds, can also act via this site, albeit at higher concentrations than is typica…
Stable expression in HEK-293 cells of the rat alpha3/beta4 subtype of neuronal nicotinic acetylcholine receptor.
The alpha3/beta4 subtype of neuronal nicotinic acetylcholine receptor (nAChR) was stably expressed in human embryonic kidney (HEK) 293 cells that co-expressed a voltage-gated Ca2+ channel. alpha3/beta4-nAChR-expressing clones were identified using the fura-2 Ca2+ imaging technique, and were further characterised by single-cell and whole-cell patch-clamp studies. Acetylcholine (ACh) induced fast activating currents which showed desensitisation and inward rectification. The conductance of the ACh-activated channel was 29 pS. The order of potency of the nicotinic agonists tested was cytisine approximately = nicotine > acetylcholine. The EC50 value for ACh was 145 microM; the Hill coefficient w…
Neuronal Nicotinic Receptors in the Locust Locusta migratoria
We have identified five cDNA clones that encode nicotinic acetylcholine receptor (nAChR) subunits expressed in the nervous system of the locust Locusta migratoria. Four of the subunits are ligand-binding α subunits, and the other is a structural β subunit. The existence of at least one more nAChR gene, probably encoding a β subunit, is indicated. Based on Northern analysis and in situ hybridization, the five subunit genes are expressed. locα1, locα3, andlocβ1 are the most abundant subunits and are expressed in similar areas of the head ganglia and retina of the adult locust. Because Locα3 binds α-bungarotoxin with high affinity, it may form a homomeric nAChR subtype such as the mammalian α7…
Physostigmine and Neuromuscular Transmission
Single channel studies carried out in cultured rat myoballs and cultured hippocampal neurons, and ion flux studies performed on Torpedo electrocyte membrane vesicles, showed that physostigmine (Phy), a well-established acetylcholinesterase inhibitor, interacts directly with nicotinic acetylcholine receptors (nAChR). Low concentrations (0.1 microM) of Phy activate the receptor integral channel, whereas higher concentrations blocked the channel in its opened state. In contrast to channel activation by acetylcholine (ACh) and classical cholinergic agonists, however, Phy was capable of activating the nAChR channel even when the ACh binding sites were blocked by competitive antagonists, such as …