MODULATION OF ACTIVITY AND PLASTICITY OF CHOLINORECEPTORS ON THE NEURONS OF A SNAIL BY AMIRIDINE AND FACRINE - PHENOMENON AND MECHANISMS

The effects of amiridine and tacrine on the membrane potential, activi ty and plasticity of cholinoreceptors have been studied using the reco rding of intracellular and transmembrane currents in identified neuron s of Helix lucorum. Amiridine and tacrine (1 - 100 mcM) have no notice able effects on the membrane potential of the cells. Both compounds mo dulate the activity of cholinoreceptors to judge from their influence on the inward current induced by the local acetylcholine (ACh) applica tion: they increase the duration of the current with a two-phase effec t on the amplitude (a short-latent intensification with a following de crease). Amiridine and tacrine intensify ACh current extinction induce d by repeated ACh application to the soma. Acetylcholinesterase inhibi tor physostigmine has a similar modulating effect on ACh current and i ts extinction. It impedes the modulating effects of amiridine and tacr ine. Amiridine and physostigmine directly affect cholinoreceptors and ion channels controlled by them changing in a similar way the current- voltage curves of ACh-current and approximating it to the equilibrium potential of chloride ions. Modulating effects of amiridine, tacrine a nd physostigmine on the activity and plasticity of cholinoreceptors ma y be supposed to be caused by their direct membrane-cytoplasmic action .