Drug interactions at the motor endplate.

The effect of bath applied agonists and reversible and irreversible antagonists upon the endplate currents produced by agonists applied either iontophoretically or in the bath was studied quantitatively. Agonist-agonist interaction (both potentiation and inhibition) can be accounted for satisfactorily by postulating independent binding and conformation change in 2 equivalent receptor subunits. With tubocurarine only slight deviations from competitive inhibition of agonist binding were detected. The action of bungarotoxin was in good agreement with this model and was studied kinetically.