Relaxation experiments using bath‐applied suberyldicholine.

Abstract

The effect of step changes in membrane potential on the endplate conductance change produced by bath-applied suberyldicholine was studied in voltage-clamped frog [Rana esculenta and R. temporaria] muscle fibers. The suberyldicholine-induced conductance increased exponentially from its provious equilibrium level to a new equilibrium level following a step hyperpolarization. For low suberyldicholine concentrations the time constant of this relaxation was independent of the concentration. For low suberyldicholine concentrations the voltage dependence of equilibrium conductance and relaxation time constants was identical. Bungarotoxin pretreatment did not affect the responses beyond a simple reduction in their amplitude. The conductance evoked by high suberyldicholine concentrations was less voltage-sensitive than that evoked by low concentrations. A new model for explaining noise and relaxation data was proposed. This postulates rate-limiting binding steps followed by a voltage-dependent isomerization.