Octanol reduces end-plate channel lifetime

Abstract

1. Post-synaptic effects of n-octanol at concentrations of 0.1-1 mM were examined in toad sartorius muscles by use of extracellular and voltage-clamp techniques.2. Octanol depressed the amplitude and duration of miniature end-plate currents and hence depressed neuromuscular transmission.3. The decay of miniature end-plate currents remained exponential in octanol solutions even when the time constant of decay (tau(D)) was decreased by 80-90%.4. The lifetime of end-plate channels, obtained by analysis of acetylcholine noise, was also decreased by octanol. The average lifetime measured from noise spectra agreed reasonably well with the time constant of decay of miniature end-plate currents, both in control solution and in octanol solutions.5. Octanol caused a reduction in the conductance of end-plate channels. Single channel conductance was on average about 25 pS in control solution and 20 pS in octanol.6. In most cells the normal voltage sensitivity of the decay of miniature end-plate currents was retained in octanol solutions. The lifetime of end-plate channels measured from acetylcholine noise also remained voltage-sensitive in octanol solutions. In some experiments in which channel lifetime was exceptionally reduced the voltage sensitivity was less than normal.7. In octanol solutions, tau(D) was still very sensitive to temperature changes in most cells although in some the temperature sensitivity of tau(D) was clearly reduced. Changes in tau(D) with temperature could generally be fitted by the Arrhenius equation suggesting that a single step reaction controlled the decay of currents both in control and in octanol solutions. In some cells in which tau(D) became less than 0.3 ms, the relationship between tau(D) and temperature became inconsistent with the Arrhenius equation.8. As the decay of end-plate currents in octanol solutions remains exponential, and the voltage and temperature sensitivity can be unchanged even when tau(D) is significantly reduced, it seems likely that octanol decreases tau(D) by increasing the rate of the reaction which normally controls the lifetime of end-plate channels.