[Differences in the habituation of the nicotinic and muscarinic cholinoreceptors of Helix neuron PPa4].

Pharmacological division of the snail cholinoreceptors population of the identified neurone RPa4 by cholinoblockators of muscarine (atropine, platyphylline) and nicotine (d-tubocurarine) receptors allowed to reveal differences in the dynamics of reversible reduction of sensitivity of these receptors during their habituation to repeated iontophoretic acetylcholine applications. Maximum desensitization of nicotine receptors is weaker, develops slower and is eliminated faster after the end of rhythmic acetylcholine applications. An assumption is made that a more rapid and deeper lowering of muscarine cholinoreceptors sensitivity is due to an increase of intracellular concentration of free calcium at their activation by the agonist.