ON THE MECHANISM OF GANGLIONIC BLOCKADE BY METHACHOLINE

¹ Department of Pharmacology, School of Medicine, Tulane University, New Orleans, Louisiana

A study was made of the effects of methacholine (MCh) on the afterpotentials and synaptic potentials of the superior cervical ganglia of cats. During the hyperpolarization produced by MCh, the positive potential (PP) and positive afterpotentials (PAP) were decreased. The negative afterpotential (NAP) was increased. By contrast, the PP and PAP were increased, and the NAP decreased, during the late-occurring depolarization evoked by MCh. The synaptic potential of ganglia treated with hexamethonium was depressed during the hyperpolarization and depolarization phases of the response to MCh. Ganglionic hyperpolarization by p-hydroxymercuribenzoate was accompanied by an increase in the synaptic potential. Conversely, ganglionic depolarization by ouabain, potassium or barium was accompanied by a decrease in the synaptic potential. The results indicate that although MCh caused hyperpolarization of the ganglion cells, the blockade of transmission was not related directly to the hyperpolarization.