Abstract | Cloning studies suggest that there are at least five types of nicotinic receptor with different amino acid sequences. David Colquhoun and colleagues discuss pharmacological consequences of this heterogeneity. The function of the muscle type receptor has been examined in some detail, though it is only recently that the equilibrium concentration-response relationship has been determined reliably. Much less is known about neuronal nicotinic receptors, which have sequences (and probably subunit stoichiometry) that differ considerably from those of the muscle and electric organ types. They also differ considerably from the latter in their abilities to bind various toxins. The usual nicotinic antagonists, such as tubocurarine and hexamethonium, show great variability between receptor type, and between species, in the extent to which they work by competitive block or by block of the ion channel. |
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