[The blocking potencies and the mode of blockade by pentobarbital and phenobarbital, examined on various types of ACh-receptor activities (author's transl)].

The ganglion cells of Aplysia contain three types of ACh-receptors. The activation of one type produces Na+-dependent depolarization (DNa-type). The other receptors are HK- and HCl-types ; activation produces K+- and Cl--dependent hyperpolarization, respectively. Effects of pentobarbital-sodium (PB), phenobarbital-sodium (PhB), and barbituric acid (BA) on each type of receptor activity were compared with each other. ACh-induced responses were evaluated by the change in membrane conductance. PBV showed different blocking potencies for each type of receptor activity, their ratio being DNa : HCl : HK=1 : 0.5 : 0.02. PhB showed a similar potency ratio, but the potency for each type was approximately a half of PB. BA blocked neither type of receptor activities. The mode of blockade was studied by plotting dose-inhibition curve for each type of receptor activity, and found to be "noncompetitive" in all types. It was suggested that PB and PhB had much greater blocking potency for the receptor activities of "nicotinic type" than that for the "muscarinic type". It was concluded that PB does not compete with ACh for the common binding site at the receptor, but it binds to a certain allosteric site which controls the opening of ionic channels, particularly for Na+ and Cl-.