Halothane and isoflurane alter acetylcholine activated ion channel kinetics.

The effects of halothane and isoflurane on the acetylcholine activated ion channel were studied in the frog sartorius muscle using the two electrode voltage clamp technique. The miniature end-plate currents (MEPCs) were recorded and evaluated for amplitude, duration of growth phase and time constant of decay (tau). Both halothane and isoflurane decreased tau in a dose dependent manner. Depression of current amplitude was also dose dependent. The ED50 value indicates tau is more affected than the amplitude of MEPC. Biexponential decay phases were seen in a small fraction of cells exposed to a low concentration of halothane but not isoflurane. Biexponential decay, when seen, was more prominent at less negative clamped membrane potential. The normal linear relationship between membrane potential and tau was not altered by anesthetics.