Acetylcholinesterase potentiates [ 3H]fluorowillardiine and [ 3H]AMPA binding to rat cortical membranes

Abstract

In addition to its action at cholinergic synapses acetylcholinesterase (AChE) has been proposed to modulate neuronal activity by mechanisms unrelated to the hydrolysis of acetylcholine. We have investigated the effects of AChE on the binding of the specific AMPA receptor agonists ( S)-[ 3H]5-fluorowillardiine ([ 3H]FW) and [ 3H]AMPA to rat cortical membranes. Pretreatment of membranes with AChE causes a dose-dependent increase in the binding of both radiolabelled agonists with a maximal increase to ∼60% above control. This increase is completely blocked by the specific AChE inhibitors propidium, physostigmine, DFP and BW 284C51. AChE pretreatment had no effect on [ 3H]kainate binding. [ 3H]FW binding to membranes from young (15-day-old) rats is four orders of magnitude more sensitive to AChE modulation than membranes from adult rats (EC 50 values of 4×10 −5 and 0.1 unit/ml, respectively) although the total percentage increase in binding is similar. Furthermore, the AChE-induced potentiation of [ 3H]FW binding is Ca 2+- and temperature-dependent suggesting an enzymatic action for AChE in this system. Saturation binding experiments with [ 3H]FW to adult membranes reveal high and low affinity binding sites and demonstrate that the main action of AChE is to increase the B max of both sites. These findings suggest that modulation of AMPA receptors could provide a molecular mechanism of action for the previously reported effects of AChE in synapse formation, synaptic plasticity and neurodegeneration.