[The effect of affinity on the type of action of ammonium compounds on skeletal muscle cholinoreceptors].
The dependence of the mode of action (agonist or antagonist) of ammonium compounds on the acetylcholine receptors (AcR) of frog skeletal muscles on their affinity for AcR was studied in experiments on musculus rectus abdominis of Rana temporaria frogs. The mode of action of the compounds proved to be dependent on the degree of the affinity and on the character of their intermolecular interactions with the receptors. The affinity of compounds of the polymethylene-bis-trimethylammonium series is determined by electrostatic and hydrophobic interaction with the AcR. In this case compounds with a low affinity constant (Ka) are poor antagonists, compounds with high Ka are strong antagonists, and compounds with intermediate Ka are partly agonists. Compounds whose affinity is determined not only by the electrostatic and hydrophobic but also by the dipole-dipole interaction (series D compounds) are pure and strong agonists.