Halothane suppresses slow inward currents in hippocampal slices

Single-electrode voltage-clamp experiments were made on CA1 neurons in the presence of tetrodotoxin and K channel blockers. Applications of halothane (1-3% v/v) for 3-10 min caused a similar marked and reversible depression of slow inward currents (probably Ca currents) evoked by depolarizing pulses from a holding potential near -80 or near -40 mV. The peak amplitudes of the inward currents were much reduced, in a concentration-dependent manner, and they decayed more rapidly (half-decay time was shortened by a quarter). In most cases, leak conductances were diminished by halothane, making it unlikely that the suppression of inward currents was primarily caused by enhancement of outward currents. A similar inactivation of Ca currents in presynaptic terminals would explain why halothane depresses synaptic transmission.