Ouabain-sensitive and insensitive acetylcholine receptors on the membrane of the same neuron in Helix pomatia

Using internally dialyzed neurons of Helix pomatia as a model, the effect o f structural analogs of acetylcholine (ACh) were investigated for their cho linomimetic properties on A- and B-types of ACh-responses. Specifically we analyzed choline esters of N-para- and ortho-alkoxybenzoyl-beta -alanines, (CH3O-, C2H5O-, C3H7O-, iso-C3H7O-, C4H9O-, iso-C4H9O-, C5H11O-, iso-C5H11O -), (in all, 16 combinations). The compounds evoked differing sensitivities of response to factors de-activating the Na-K-pump (ouabain and K-free sol ution), Most compounds resembled ACh: ionic currents caused by these compou nds were inhibited by Na-K pump blockers in the case of A-type responses - B-type responses were insensitive to these factors. Ionic currents induced by choline esters of p-, o-propoxy- and iso-propoxybenzoyl-beta -alanines w ere insensitive to ouabain and K-free solution in the case of A- and B-type responses. Ionic currents induced by the choline ester of p-butoxybenzoyl- beta -alanine were inhibited by ouabain and K-free solution on both types o f neuron. The results allow us to classify choline eaters of p-, o-propoxy- and iso-propoxybenzoyl-beta -alanines as N-cholinomimetics, while the chol ine ester of p-butoxybenzoyl-beta -alanine can be considered as M-cholinomi metic. We conclude that both M- and N-type ACh receptors exist on the membr ane of the same neurons. (C) 2001 Elsevier Science Inc. All rights reserved .