Inhalation anaesthetics block accommodation of pyramidal cell discharge in the rat hippocampus

The effects of the three inhalation anaesthetics enflurane, isoflurane and halothane were tested in vitro on accommodation of rat CA1 neurones. At near clinical concentrations (approximately 2.5%) the anaesthetics slightly depressed antidromic field potential responses. At the same concentrations the anaesthetics also blocked accommodation reversibly and reduced the after hyperpolarization of CA1 neurones. No significant changes in the threshold potential were observed, although the resting membrane potential was often increased in the presence of the anaesthetics. The action of enflurane was not blocked by propranolol 20 mumol litre-1 and enflurane had no obvious effect on the duration of Ca2+ spikes of CA1 neurones. It is concluded that the anaesthetics may have a direct effect on membrane K+ channels such as the Ca2+-activated K+ conductance and that the block of accommodation is unlikely to account for the proconvulsant action of enflurane.