Relaxation experiments using bath-applied suberyldicholine.

1. The effect of step changes in membrane potential on the end-plate conductance change produced by bath-applied suberyldicholine was studied in voltage-clamped frog muscle fibres. 2. The suberyldicholine-induced conductance increased exponentially from its previous equilibrium level to a new equilibrium level following a step hyperpolarization. 3. For low suberyldicholine concentrations the time constant of this relaxation was independent of the concentration. 4. For low suberyldicholine concentrations the voltage dependence of equilibrium conductance and relaxation time constants was identical. 5. Bungarotoxin pretreatment did not affect the responses beyond a simple reduction in their amplitude. 6. The conductance evoked by high suberyldicholine concentrations was less voltage-sensitive than that evoked by low concentrations. 7. A new model for explaining noise and relaxation data is proposed. This postulates rate-limiting binding steps followed by a voltage-dependent isomerization.