Voltage dependence of agonist responses at voltage-clamped frog endplates

The conductance increment produced at voltage clamped frog endplates by various agonists, applied either iontophoretically or in the bath, increases exponentially with membrane hyperpolarisation, an e-fold change being obtained with shifts of the order of 100 mV. The voltage dependency of this increase is the same for different, but low, agonist concentrations. However, conductance changes evoked by decamethonium increased less with hyperpolarisation than did conductance changes evoked by carbachol or tetramethylammonium. Hyperpolarisation slowed iontophoretic responses to carbachol or decamethonium, and enhanced and prolonged inhibition of carbachol by a brief pulse of decamethonium.