Simultaneous measurements of receptor occupation and the change in ion permeability elicited by the ligands enable one to define the linkage between agonist association and activation of the ion channel. The nicotinic receptor behaves effectively as a co-operative dimer. Two agonist molecules are required for activation while a single bound antagonist is sufficient to block the response of the receptor oligomer. The two agonist binding sites on the oligomer do not show precise functional equivalence as might be anticipated from the arrangement of subunits of this protein in the membrane.
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