Octanol reduces end-plate channel lifetime

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Abstract
Postsynaptic effects of n-octanol at concentrations of 0.1-1 mM were examined in toad [Bufo marinus] sartorius muscles by extracellular and voltage-clamp techniques. Octanol depressed the amplitude and duration of miniature endplate currents and hence depressed neuromuscular transmission. The decay of miniature endplate currents remained exponential in octanol solutions even when the time constant of decay (.tau.D) was decreased by 80-90%. The lifetime of endplate 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 endplate currents, in control solution and in octanol solutions. Octanol caused a reduction in the conductance of endplate channels. Single channel conductance was on average about 25 pS [siemens] in control solution and 20 pS in octanol. In most cells the normal voltage sensitivity of the decay of miniature endplate currents was retained in octanol solutions. The lifetime of endplate 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. 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. As the decay of endplate 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 endplate channels.